# Questions tagged [sequence]

For challenges involving some sort of sequence.

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### How many unique one sided polyominos

Context From Wikipedia: A polyomino is a plane geometric figure formed by joining one or more equal squares edge to edge. one-sided polyominoes are distinct when none is a translation or rotation of ...
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### It's all about the sum of the digits

The sequence Given an integer $n>0$, we define $a(n)$ as the lowest positive integer such that there exists exactly $n$ positive integers smaller than $a(n)$ whose sum of digits is equal ...
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### Concentric rings on a snub square tiling

This challenge takes place on the snub square tiling. Start by choosing any triangle, and color it $c_1$. Next, find all tiles which touch this triangle at any vertex, and color them $c_2$. Next,...
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### Number of palindrome splits

In this task you will take as input a non-negative integer $n$, and output the number of pairs of non-negative integers $a,b$ such that both are palindromes*, $a \leq b$, and $a+b = n$. For ...
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### Counts Of Orderings Containing At Most K Of The Kth Class

This challenge is about the number of orderings which contain at most $n$ classes and at most $k$ of the $k^{\text{th}}$ class. One way to represent such an ordering is as a sequence of ...
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### What's my telephone number?

Introduction The telephone numbers or involution numbers are a sequence of integers that count the ways $n$ telephone lines can be connected to each other, where each line can be connected to at ...
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### Cutting Sequence for N dimensions

Inputs: The program or function should take 2 vector-like (e.g. a list of numbers) O and V of the same number of dimensions, and a number T (all floating-point numbers or similar) Constraints: T >=...
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### Smallest number such that concatenation is a square

Challenge Write a program or function that takes a number $n$ and returns the smallest $k$ such that concatenation $n'k$ is a square. This sequence is described by A071176 on the OEIS. I/O ...
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### Partitioning Digits into Distinct Integers

Given a sequence of base-10 digits, output the longest list of integers that contains all the digits exactly once, in the order in which they appeared in the input, without repeating any integers. ...
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### Shorten String as Much as Possible [closed]

Introduction In a list of strings, there is a certain length you can shorten strings to before they become indistinguishable. This is a pretty bad explanation, so here is an example. ...
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### How Shuffled is this Sequence?

Given a sequence $S$ with length $n$ of exactly one each of whole numbers from $1$ to $n$, your task is to return a number $\sigma$ indicating how shuffled it is. Definition of shuffledness ...
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### Maximal 2-distance Sets

In the plane ($\mathbb R^2$) we can have at most five distinct points such that the distances from each point to every other point (except itself) can assume at most two distinct values. An example ...
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### N-Dimensional Cartesian Product

Introduction The Cartesian product of two lists is calculated by iterating over every element in the first and second list and outputting points. This is not a very good definition, so here are some ...
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### What's this constructed number's starter?

A number of programming languages construct large integers through 'concatenating' the digit to the end of the existing number. For example, Labyrinth, or Adapt. By concatenating the digit to the end, ...
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### Count the number of triangles

Given a list of positive integers, find the number of triangles we can form such that their side lengths are represented by three distinct entries of the input list. (Inspiration comes from CR.) ...
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### Count the number of shortest paths to n

This code challenge will have you compute the number of ways to reach $n$ starting from $2$ using maps of the form $x \mapsto x + x^j$ (with $j$ a non-negative integer), and doing so in the ...
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### Crossing sequences

Crossing Sequences Given a list of positive integers A, call it an increasing sequence if each element is greater than or equal to the previous one; and call it a ...
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### Inverse Colombian Function

Let's define a sequence: The n digit summing sequence (n-DSS) is a sequence that starts with n. If the last number was k, then the next number is k + digit-sum(k). Here are the first few n-DSS: ...
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### Draw Recamán's sequence with ASCII

Recamán's sequence (A005132) is a mathematical sequence, defined as such: A(n) = \begin{cases}0 & \textrm{if } n = 0 \\ A(n-1) - n & \textrm{if } A(n-1) - n \textrm{ is positive and not ...
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### Find the hardest OEIS sequence to golf!

Notice: This question originally had people write comments with a shorter program, rather than new answers. This has been changed so that people with shorter programs can get reputation too. Hopefully ...
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### Reverse your code, reverse the OEIS

The task here is to write a program that takes an natural number, $n$, and produces the $n$th term of an OEIS sequence. That sequence should have an identifier in the form of ...
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### Robbers: The Hidden OEIS Substring

This is a Cops and Robbers challenge. This is the robber's thread. The cop's thread is here. The cops will pick any sequence from the OEIS, and write a program p that prints the first integer from ...
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### Cops: The Hidden OEIS Substring

This is a Cops and Robbers challenge. This is the cop's thread. The robber's thread is here. As a cop, you must pick any sequence from the OEIS, and write a program p that prints the first integer ...
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### Mutation chain generator [duplicate]

Given a start word and a target word, print the "mutation chain" that starts at the start word and ends at the target word. You may assume both words are lowercase and only have alphabetic characters....
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### Counting generalized polyominoes

This challenge will have you count pseudo-polyforms on the snub square tiling. I think that this sequence does not yet exist on the OEIS, so this challenge exists to compute as many terms as possible ...
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### Two palindromes are not enough

Some numbers, such as $14241$, are palindromes in base 10: if you write the digits in reverse order, you get the same number. Some numbers are the sum of 2 palindromes; for example, $110=88+22$, ...
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### Output the nth 'boring' number

There are 9 main types of numbers, if you categorise them by the properties of their factors. Many numbers fall into at least one of these categories, but a few don't. The categories are as follows: ...
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### First occurrence in the Sixers sequence

The Sixers sequence is a name that can be given to sequence A087409. I learned about this sequence in a Numberphile video, and it can be constructed as follows: First, take the multiples of 6, ...
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### Nth term of Van Eck Sequence

Output the Nth term of the Van Eck Sequence. Van Eck Sequence is defined as: Starts with 0. If the last term is the first occurrence of that term the next term is 0. If the last term has occurred ...
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### An OEIS polyglot

This is an answer-chaining challenge relating to the OEIS. Oh, the justification for this is because a company needs one program to print out their OEIS sequences real bad and they have every ...
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### Hostile Divisor Numbers

Some divisors of positive integers really hate each other and they don't like to share one or more common digits. Those integers are called Hostile Divisor Numbers (HDN) Examples Number <...