Amicable pairs
editable example
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ghul
use IO.Std.write_line
use Ghul.Pipes
let limit = 20000
sum_of_proper_divisors(n: int) -> int =>
(1::(n / 2))
|> filter(divisor => n % divisor == 0)
|> reduce(0, (total, divisor) => total + divisor)
(1::limit)
|> map(n => (n, partner = sum_of_proper_divisors(n)))
|> filter(((n, partner)) =>
partner > n /\ sum_of_proper_divisors(partner) == n)
|> each(((n, partner)) => write_line("{n} and {partner}"))