# 2 factors factorization

Given a natural number n write a program or function to get a list of all the possible two factors multiplications that can be used to achieve n. To understand better what is pretended you can go to http://factornumber.com/?page=16777216 to see when n is 16777216 we get the following list:

   2 × 8388608
4 × 4194304
8 × 2097152
16 × 1048576
32 ×  524288
64 ×  262144
128 ×  131072
256 ×   65536
512 ×   32768
1024 ×   16384
2048 ×    8192
4096 ×    4096


No need to pretty print things like here. The requirement is that each entry (pair of factors) is well distinguished from each other and inside each pair, the first factor is also well distinguished from the other. If you choose to return a list/array, the inside element can be a list/array with two elements, or some structure of your language that supports a pair of things like C++ std::pair.

Do not print the multiplication by 1 entry, nor repeat entries with the first factor commuted by the second, as they are pretty useless.

No winner; it will be a per language basis code golf.

• Could you possibly add a smaller test case, such as 30? Dec 2, 2017 at 22:27
• @cairdcoinheringaahing You can use factornumber.com to generate more test cases. Dec 2, 2017 at 22:39
• I've seen this "per language" competition recently. What's the point? Most Qs don't get more than 1 or 2 As per language, and you still can select just one A as correct. Dec 2, 2017 at 23:54
• @fedes. It's usually because there's no point in comparing between languages (i.e. Java vs. Jelly). Dec 3, 2017 at 0:06
• @totallyhuman yeah, I know. Most of my answers are in Factor, or even Smalltalk. No chance against the golfing languages. Maybe there could be some way of ranking languages by verbosity and boilerplatery Dec 3, 2017 at 0:28

# Pyt, 67 65 bytes

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I'm pretty sure this can be golfed.

Basically, the algorithm generates a list of all of the divisors of the input (let's call it n), makes the same list, but flipped, interleaves the two (e.g., if n=24, then, at this point, it has [1,24,2,12,3,8,4,6,6,4,8,3,12,2,24,1]), and prints out the elements from index 2 until half the array length, printing each number on a new line, and with an extra new line in between every pair.

Most of the work is done in actually managing the stack.

Saved 2 bytes by using increment function.

# Perl 5, 50 bytes

sub{map[$_,$_[0]/$_],grep!($_[0]%$_),2..sqrt$_[0]}


Ungolfed:

sub {
return map  { [$_,$_[0] / $_] } grep { !($_[0] % $_) } (2 .. sqrt($_[0]));
}


# Japt, 9 bytes

Outputs a 2D array.

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Try it