func cuban_primes(n) {
    1..Inf -> lazy.map {|k| 3*k*(k+1) + 1 }\
                  .grep{ .is_prime }\
                  .first(n)
}

cuban_primes(200).slices(10).each {
    say .map { "%9s" % .commify }.join(' ')
}

say ("\n100,000th cuban prime is: ", cuban_primes(1e5).last.commify)