abduct ~/crystal-0.13.0-1/bin $ time ./test

real 0m2.298s
user 0m2.295s
sys 0m0.004s
abduct ~/crystal-0.13.0-1/bin $ time ruby ./test.rb

real 1m13.979s
user 1m13.962s
sys 0m0.016s

def prime_test(max)
primes = [] of Int32
(1..max).each {|num|
if (2..num-1).all? {|denom| num%denom >0}
primes.push(num)
end
}
end

prime_test(100000)