Automate the OEIS

Question

We see a lot of challenges here asking for a function to create a sequence from the OEIS. While these challenges are fun, as a programmer I see an opportunity for automation.

Your challenge is to make a program that takes the index of a sequence (e.g. A172141) and some integer n (e.g. 7), and pulls the appropriate value from the appropriate webpage.

I/O

As mentioned, your program should take a sequence index and some value n as input and output the nth term in that sequence. You accept any index in the sequence's B-files. If the index is greater than the largest index listed in the B-files you may throw an exception or output whatever you choose (these are not in the test cases). Standard methods of input and output are permitted.

Restrictions on web use

You should not access any websites other than https://oeis.org and http://oeis.org. This includes url shorteners, your own personal website, and this question itself. If you would like to access some other website and you believe that it is not unfair to allow you to do so, you can leave a comment and I will arbitrate.

Scoring

This is a code golf challenge so the program with the least bytes used in its source code wins. Standard loopholes are disallowed.

Test Cases

Assuming that your machine has proper internet connection and the OEIS servers are up and running the following inputs and outputs should correspond.

A172141, 7   -> 980
A173429, 4   -> 276
A190394, 6   -> 16
A002911, 11  -> 960
A052170, 3   -> 24
A060296, 8   -> 3
A178732, 5   -> 27
A000001, 1   -> 1
A000796, 314 -> 3
A001622, 162 -> 8
A002206, -1  -> 1

Tip

When accessing the B-files http://oeis.org/b<A-number>.txt will redirect to the proper B-file.

It's not clear to me up which indices we have to support. The last two test cases hint that we should query, e.g., oeis.org/A000796/b000796.txt rather than oeis.org/A000796/list. Is the fomer what you mean by B-files? In that case, mentioning the offset is rather superfluous. — Dennis, Aug 10, 2016 at 16:35
@Dennis Sorry I think that was the result of multiple edits over time. I will edit for clarity, — Wheat Wizard, Aug 10, 2016 at 16:38
I think this should have spent more time in the sandbox, because I'm sure it wasn't your intention that sequences without B-files should be unsupported. — Peter Taylor, Aug 10, 2016 at 18:24
@PeterTaylor according to the OeisWiki "If no b-file has been uploaded for a particular sequence, the server generates a b-file containing exactly the terms displayed, for convenience with automated tools." so there should be a B-file for every sequence. Although you may be right about prematurely moving this challenge from the sandbox. — Wheat Wizard, Aug 10, 2016 at 18:29

Dennis · Accepted Answer · 2016-08-10 17:44:53Z

Bash + coreutils + w3m, 51 45 42 bytes

w3m oeis.org/b${1:1}.txt|sed "s/^$2 //p;d"

Thanks to @EamonOlive for golfing off 3 bytes!

Example run

$ bash oeis.sh A172141 7
980

How it works

w3m is a text-based web browser, which displays both HTML and plain text in readable format. Unlike curl, it follows redirects by default (this is required, since oeis.org/bxxxxxx.txt redirects to oeis.org/Axxxxxx/bxxxxxx.txt), doesn't produce any stray output to STDERR, and has a three-byte name.

The command

w3m oeis.org/b${1:1}.txt

the desired URL, where ${1:1} is the first command-line argument without its first character.

The output is piped to the command

sed "s/^$2 //p;d"

which extracts the desired output. s/^$2 //p attempts to replace ^$2 (start of line, followed by the second command-line argument, followed by a space) with the empty string. If the substitution is successful, p prints its result. Afterwards, d unconditionally deletes the pattern to prevent sed from printing the entire input.

You can save a few bytes by using oeis.org/b${1:1}.txt instead of oeis.org/$1/b${1:1}.txt — Wheat Wizard, Aug 10, 2016 at 16:35
Heh, I would normally have used sed -n ..., but that would be one more character. — Vatine, Aug 11, 2016 at 11:19
@Vatine With -n, the double quotes could be replaced with an escaped space, for the same byte count. — Dennis, Aug 11, 2016 at 17:27

Community · Accepted Answer · 2020-06-17 09:04:33Z

4

Mathematica + OEIS.m, 31

(OEISFunction@ToString@#;#@#2)&

example usage: %[A172141,36]

Mathematica, 85

#2/.Rule@@@Import["http://oeis.org/b"<>#~StringDrop~1<>".txt","Data"]~DeleteCases~{}&

example usage: %["A002206",-1]

edited Jun 17, 2020 at 9:04

CommunityBot

1

answered Aug 11, 2016 at 23:12

dbanet

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Community · Accepted Answer · 2017-04-13 12:39:07Z

3

Perl, 59 bytes

($_,$v)=@ARGV;/./;say`curl oeis.org/$_/b$'.txt`=~/$v (.*)/m

Needs -M5.010 or -E to run. For instance :

$ cat oeis.pl
($_,$v)=@ARGV;/./;say`curl oeis.org/$_/b$'.txt`=~/$v (.*)/m
$ perl -M5.010 oeis.pl A178932 5 2>&-
27

Saved 8 bytes thanks to @Dennis answer, by removing http://, as he did.

edited Apr 13, 2017 at 12:39

CommunityBot

1

answered Aug 10, 2016 at 16:05

Dada

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Dennis · Accepted Answer · 2016-08-10 16:52:53Z

2

CJam, 36 bytes

"oeis.org/b"r1>+".txt"+gN%Sf%z~\ra#=

Example run

$ cjam oeis.cjam <<< 'A172141 7'
980

answered Aug 10, 2016 at 16:52

Dennis

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Community · Accepted Answer · 2020-06-17 09:04:33Z

2

Python 2, 125 118 113 bytes

7 12 bytes saved thanks to Lynn

import re,urllib2 as u;lambda x,y:re.findall("(?<=%d ).*"%y,u.urlopen("http://oeis.org/b%s.txt"%x[1:]).read())[0]

Well heres my go at my own problem. It is likely suboptimal but I think I did a pretty decent job. It creates an anonymous function that takes a string and integer as arguments and returns a string as the result or throws an error if the index is out of range.

This can be made into a 124 bytes full program.

import re,urllib2 as u;print re.findall("(?<=%d ).*"%input(),u.urlopen("http://oeis.org/b%s.txt"%raw_input()[1:]).read())[0]

This prompts the user for the input. First asking for the index and then the A-number of the sequence.

edited Jun 17, 2020 at 9:04

CommunityBot

1

answered Aug 10, 2016 at 16:17

Wheat Wizard♦

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\$\begingroup\$ Some tiny saves: import re,urllib2 as u;lambda x,y:re.search("%d (.*)\n"%y,u.urlopen("http://oeis.org/b%s.txt"%x[1:]).read()).group(1) \$\endgroup\$
– Lynn
Aug 10, 2016 at 16:39
\$\begingroup\$ And lambda x,y:re.split("%d (.*)"%y,u.urlopen("http://oeis.org/b%s.txt"%x[1:]).read())[1] is shorter still! \$\endgroup\$
– Lynn
Aug 10, 2016 at 16:45

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Leaky Nun · Accepted Answer · 2016-08-10 17:02:17Z

2

Python 3, 153 146 135 bytes

7 bytes thanks to FryAmTheEggman.

6 bytes thanks to Eamon Olive.

5 bytes thanks to Rod.

from urllib.request import*
def f(a,n):
 for l in urlopen("http://oeis.org/b%s.txt"%a[1:]):
  p,q=l.split()
  if n==p.decode():return q

Call it like this:

print(f("A000796","314"))

Run on a machine where the default is utf-8.

edited Aug 10, 2016 at 17:02

answered Aug 10, 2016 at 15:43

Leaky Nun

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1

\$\begingroup\$ In my opinion requiring a string for one argument, and a byte array for another is too lenient an input format, and you should just add the bytes required to encode into bytes yourself. Nothing about this challenge makes it reasonable to require raw bytes as input. \$\endgroup\$
– orlp
Aug 10, 2016 at 15:49
\$\begingroup\$ Can’t you change A%s to %s and then the first a[1:] to a? \$\endgroup\$
– Lynn
Aug 10, 2016 at 15:52
\$\begingroup\$ @orlp Alright, done. \$\endgroup\$
– Leaky Nun
Aug 10, 2016 at 15:55
\$\begingroup\$ @Lynn Yes, because apparently I'm stupid. \$\endgroup\$
– Leaky Nun
Aug 10, 2016 at 15:55
1

\$\begingroup\$ @FryAmTheEggman Yes and no. The default is the environment's locale. \$\endgroup\$
– Dennis
Aug 10, 2016 at 15:59

| Show 3 more comments

Samsquanch · Accepted Answer · 2016-08-10 19:36:34Z

2

PHP 5.6, 93 92 bytes

function f($i,$l){echo explode(' ',file('http://oeis.org/b'.substr($i,1).'.txt')[--$l])[1];}

This one is pretty straight forward. Pull the page with file(), get the line at $line - 1 (0-index), explode on the space and print out the second array element from that.

edited Aug 10, 2016 at 19:36

answered Aug 10, 2016 at 17:34

Samsquanch

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Copper · Accepted Answer · 2016-08-10 22:30:07Z

Nim, 123 115 113 bytes

import httpclient,nre,future
(a,n)=>get getContent("http://oeis.org/b"&a[1..^0]&".txt").find re "(?<="&n&r" )\d+"

This is a lambda expression; to use it, it must be passed as an argument to a testing procedure. A complete program that can be used for testing is given here:

import httpclient,nre,future
proc test(x: (string, string) -> RegexMatch) = echo x("A172141", "7") # Your input here
test((a,n)=>get getContent("http://oeis.org/b"&a[1..^0]&".txt").find re "(?<="&n&r" )\d+")

Expects input as two strings. Example usage:

$ nim c oeis.nim
$ ./oeis
980

We use httpclient's getContent proc to get the OEIS b-file, then use a regex to find the line with the index. find returns an Option[RegexMatch], so we use get to retrieve the value from the Option. echo automatically stringifies, so we leave stringification out.

Community · Accepted Answer · 2017-04-13 12:39:12Z

2

R, 94 89 bytes

t=read.table(paste0("http://oeis.org/b",substring(scan(,""),2),".txt"));t[t$V1==scan(),2]

Using sprintf instead of paste0 results in the same bytecount:

t=read.table(sprintf("http://oeis.org/b%s.txt",substring(scan(,""),2)));t[t$V1==scan(),2]

Five bytes saved thanks to plannapus.

edited Apr 13, 2017 at 12:39

CommunityBot

1

answered Aug 10, 2016 at 16:57

pajonk

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\$\begingroup\$ Too bad you can library(stringr) for free and use str_sub for -2 bytes ^^ \$\endgroup\$
– AlexR
Aug 11, 2016 at 13:52
\$\begingroup\$ @AlexR I don't think I can import a library for free ;-) \$\endgroup\$
– pajonk
Aug 12, 2016 at 17:40
\$\begingroup\$ Oops, there was a typo in my comment -- Too bad you can't. It was just a first thought for golfing, because stringr is one of my default packages loaded in the .Rprofile of all my projects. \$\endgroup\$
– AlexR
Aug 12, 2016 at 17:41
1

\$\begingroup\$ You don't need to use url, argument file of read.table can be the URL as a character string. \$\endgroup\$
– plannapus
Dec 26, 2016 at 10:16
\$\begingroup\$ @plannapus Indeed, that's right. Thanks! \$\endgroup\$
– pajonk
Dec 26, 2016 at 19:01

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NikoNyrh · Accepted Answer · 2016-12-25 19:26:06Z

1

Clojure, 103

#(read-string((re-find(re-pattern(str %2" (\\d+)"))(slurp(str"http://oeis.org/b"(subs % 1)".txt")))1)))

re-find finds a vector of first matche's regex groups, it is used as a function and 1 gets the string at position 1. read-string converts string to int. I'm not 100% sure if this regex always finds the correct row.

answered Dec 25, 2016 at 19:26

NikoNyrh

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Community · Accepted Answer · 2020-06-17 09:04:33Z

1

R, 87 bytes

f=function(A,n)(R<-read.table(gsub("A(\\d+)","http://oeis.org/b\\1.txt",A)))[R$V1==n,2]

Build the URL string with regexes instead of paste or sprintf.

edited Jun 17, 2020 at 9:04

CommunityBot

1

answered Dec 26, 2016 at 10:27

plannapus

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Community · Accepted Answer · 2020-06-17 09:04:33Z

0

Node.js + `request`, 109 bytes

x=>n=>require('request')(`http://oeis.org/b${x.slice(1)}.txt`,(a,b)=>console.log(b.body.match(n+` (.+)`)[1]))

Takes the sequence ID and a number.

edited Jun 17, 2020 at 9:04

CommunityBot

1

answered Aug 10, 2016 at 19:04

Mama Fun Roll

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Community · Accepted Answer · 2020-06-17 09:04:33Z

0

Julia, 88 bytes

x\y=match(Regex("$y (.*)"),readall(Requests.get("http://oeis.org/b$(x[2:end]).txt")))[1]

Golfed with some help from @Dennis!

Make sure you have Requests.jl installed before running.

edited Jun 17, 2020 at 9:04

CommunityBot

1

answered Aug 11, 2016 at 0:44

Mama Fun Roll

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downrep_nation · Accepted Answer · 2016-08-11 22:06:34Z

0

ListSharp, 266 bytes

STRG a=READ[<here>+"\\a.txt"]
ROWS x=ROWSPLIT a BY [","]
STRG a=GETRANGE x[0] FROM [2] TO [a LENGTH]
NUMB y=<c#int.Parse(x[1])c#>
STRG a=DOWNLOAD["http://oeis.org/b"+a+".txt"]
ROWS x=ROWSPLIT a BY [<newline>]
STRG a=GETLINE x [y]
ROWS x=ROWSPLIT a BY [" "]
SHOW=x[1]

Its sad when a language made for web scraping needs so many lines because nesting statements in ListSharp is taboo

answered Aug 11, 2016 at 22:06

downrep_nation

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Makonede · Accepted Answer · 2021-05-12 23:23:50Z

05AB1E, 29 bytes

¦’ÏÁ€ˆ.µÔ/bÿ.í¼t’.w¶¡€#˜DIk>è

Beats all other answers.

¦’...’.w¶¡€#˜DIk>è  # trimmed program
                 è  # 0-based...
               k    # 0-based index of...
              I     # input...
               k    # in...
            ˜D      # flattened list of...
      .w            # content of response from url...
                    # (implicit) "http://" concatenated with...
 ’...’              # "oeis.org/bÿ.txt"...
                    # (implicit) with ÿ replaced by...
                    # implicit input...
¦                   # excluding the first character...
         ¡          # split by...
        ¶           # newlines...
          €         # with each element...
           #        # split by spaces...
                >   # plus 1...
                 è  # th element in...
            ˜       # flattened list of...
      .w            # content of response from url...
                    # (implicit) "http://" concatenated with...
 ’...’              # "oeis.org/bÿ.txt"...
                    # (implicit) with ÿ replaced by...
                    # implicit input...
¦                   # excluding the first character...
         ¡          # split by...
        ¶           # newlines...
          €         # with each element...
           #        # split by spaces

Stack Exchange Network

Automate the OEIS

I/O

Restrictions on web use

Scoring

Test Cases

Tip

15 Answers 15

Bash + coreutils + w3m, 51 45 42 bytes

Example run

How it works

Mathematica + OEIS.m, 31

Mathematica, 85

Perl, 59 bytes

CJam, 36 bytes

Example run

Python 2, 125 118 113 bytes

Python 3, 153 146 135 bytes

PHP 5.6, 93 92 bytes

Nim, 123 115 113 bytes

R, 94 89 bytes

Clojure, 103

R, 87 bytes

Node.js + `request`, 109 bytes

Julia, 88 bytes

ListSharp, 266 bytes

05AB1E, 29 bytes

Your Answer

Not the answer you're looking for? Browse other questions tagged
code-golf
sequence
internet
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Linked

Hot Network Questions

Automate the OEIS

I/O

Restrictions on web use

Scoring

Test Cases

Tip

15 Answers 15

Bash + coreutils + w3m, 51 45 42 bytes

Example run

How it works

Mathematica + OEIS.m, 31

Mathematica, 85

Perl, 59 bytes

CJam, 36 bytes

Example run

Python 2, 125 118 113 bytes

Python 3, 153 146 135 bytes

PHP 5.6, 93 92 bytes

Nim, 123 115 113 bytes

R, 94 89 bytes

Clojure, 103

R, 87 bytes

Node.js + request, 109 bytes

Julia, 88 bytes

ListSharp, 266 bytes

05AB1E, 29 bytes

Your Answer

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Node.js + `request`, 109 bytes

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