project-euler/Sidef/443 GCD sequence.sf

#!/usr/bin/ruby

# Author: Trizen
# Date: 03 September 2019
# Translated: 16 November 2023
# https://github.com/trizen

# https://projecteuler.net/problem=443

# Runtime: 1 minute, 28 seconds

func GCD_sequence (upto) {

    var sum = 13

    for (var n = 5; n <= upto; ++n) {
        if (n >= 100 && !n.is_coprime(sum)) {

            var k = (n + (n - 1))
            sum += gcd(n, sum)

            if (k.is_prime) {

                if (k >= upto) {
                    sum += (upto - n)
                    break
                }

                sum += (k - (n - 1))
                n = k
            }
        }
        else {
            sum += gcd(n, sum)
        }
    }

    return sum
}

assert_eq(GCD_sequence(1000), 2524)
assert_eq(GCD_sequence(1000000), 2624152)

say GCD_sequence(1000000000000000)