sidef-scripts/Math/is_even_perfect_2.sf

#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# License: GPLv3
# Date: 12 December 2016
# https://github.com/trizen

# An efficient verification for an even perfect number.

func is_even_perfect(n) {
    var v = valuation(n, 2) || return false
    var m = 1+(n >> v)
    (m &  (m-1)).is_zero    || return false
    (m >> (v+1)).is_one     || return false
    is_mersenne_prime(v+1)
}

say is_even_perfect(191561942608236107294793378084303638130997321548169216)                            # true
say is_even_perfect(191561942608236107294793378084303638130997321548169214)                            # false
say is_even_perfect(191561942608236107294793378084303638130997321548169218)                            # false
say is_even_perfect(14474011154664524427946373126085988481573677491474835889066354349131199152128)     # true

# A much larger perfect number
say is_even_perfect(141053783706712069063207958086063189881486743514715667838838675999954867742652380114104193329037690251561950568709829327164087724366370087116731268159313652487450652439805877296207297446723295166658228846926807786652870188920867879451478364569313922060370695064736073572378695176473055266826253284886383715072974324463835300053138429460296575143368065570759537328128)

# Search test
for n in (1..10000) {
    is_even_perfect(n) && say n
}