project-euler/Sidef/046 Goldbach s other conjecture.sf

#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# Edit: 25 July 2021
# https://github.com/trizen

# What is the smallest odd composite that cannot be written as the sum of a prime and twice a square?

# https://projecteuler.net/problem=46

# Runtime: 0.307s

3..Inf `by` 2 -> lazy.grep{ .is_composite }.each {|n|

    1..isqrt(n>>1) -> any {|i|
        is_prime(n - 2*i*i)
    } && next

    say n
    break
}