Prime finder in crystal-lang

prime.cr

require "math"

NUMBER_OF_PRIMES = 1500000
primes = [2]
test_number = 2
primes_found = 0

while primes_found < NUMBER_OF_PRIMES
  test_primitiveness = true
  i = 0
  while (primes.size > i && primes[i] <= Math.sqrt(test_number) && test_primitiveness)
    if test_number % primes[i] == 0
      test_primitiveness = false
    end
    i += 1
  end
  if test_primitiveness
    primes << test_number
    primes_found += 1
  end
  test_number += 1
end

Test run on Intel(R) Core(TM) 2 Quad Q9400 @ 2.66GHz with Crystal 0.11.1:

[z2s8@Sherman crystal-mine]$ crystal build --release prime.cr 
[z2s8@Sherman crystal-mine]$ time ./prime 

real    0m4.932s
user    0m4.925s
sys     0m0.009s
[z2s8@Sherman crystal-mine]$ time ./prime 

real    0m4.911s
user    0m4.900s
sys     0m0.013s
[z2s8@Sherman crystal-mine]$ time ./prime 

real    0m4.919s
user    0m4.911s
sys     0m0.010s
[z2s8@Sherman crystal-mine]$ du -h prime
268K    prime