func is_curzon(n, k) {
    powmod(k, n, k*n + 1).is_congruent(-1, k*n + 1) && (n > 0)
}

for k in (2 .. 10 `by` 2) {
    say "\nFirst 50 Curzon numbers using a base of #{k}:"
    say 50.by {|n| is_curzon(n, k) }.join(' ')
    say ("1000th term: ", 1000.th {|n| is_curzon(n,k) })
}