Problem Statement

Two integers

N

{\displaystyle N}

and

M

{\displaystyle M}

are said to be amicable pairs if

N ≠ M

{\displaystyle N\neq M}

and the sum of the proper divisors of

N

{\displaystyle N}

(

s u m

(

p r o p D i v s

( N ) )

{\displaystyle \mathrm {sum} (\mathrm {propDivs} (N))}

)

= M

{\displaystyle =M}

as well as

s u m

(

p r o p D i v s

( M ) )

N

{\displaystyle \mathrm {sum} (\mathrm {propDivs} (M))=N}

.

1184 and 1210 are an amicable pair, with proper divisors:

Calculate and show here the Amicable pairs below 20,000; (there are eight).

Let's start with the solution:

import: mapping

Integer method: properDivs -- []
   #[ self swap mod 0 == ] self 2 / seq filter ;
 
: amicables
| i j |
   Array new
   20000 loop: i [
      i properDivs sum dup ->j i <= if continue then
      j properDivs sum i <> if continue then
      [ i, j ] over add
      ]
;