factorization_of_fibonacci_numbers.sf

#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# Date: 23 April 2019
# https://github.com/trizen

# Find factors of Fibonacci numbers, using the property:
#
#   d|n => F(d)|F(n)
#
# where F(n) is the n-th Fibonacci number.

# See also:
#   https://en.wikipedia.org/wiki/Fibonacci

func factor_fibonacci(n) {

    var acc = 1
    var factors = []

    n.divisors.each {|d|
        var f = d.fibonacci
        var t = f/gcd(acc, f)
        factors << t if (t > 1)
        acc *= f
    }

    var u = factors.prod
    var v = n.fibonacci

    if (v > u) {
        factors << v/u
    }

    factors.sort
}

for k in (3..6) {
    say ("F(#{k}!) = ", factor_fibonacci(k!))
}

__END__
F(3!) = [2, 4]
F(4!) = [2, 3, 4, 7, 12, 23]
F(5!) = [2, 3, 4, 5, 7, 11, 12, 23, 31, 41, 61, 2161, 2521, 4974481]
F(6!) = [2, 3, 4, 5, 7, 11, 17, 19, 23, 31, 41, 47, 61, 72, 107, 1103, 2161, 2521, 97921, 103681, 109441, 4868641, 4974481, 10749957121, 10783342081, 23735900452321, 115562692701892638721, 13354478339945439424243379671493453537281]