Pascal's triangle

func catalan(num) {
  var t = [0, 1]
  (1..num).map { |i|
    flip(^i    ).each {|j| t[j+1] += t[j] }
    t[i+1] = t[i]
    flip(^i.inc).each {|j| t[j+1] += t[j] }
    t[i+1] - t[i]
  }
}

say catalan(15).join(' ')

Output:

1 2 5 14 42 132 429 1430 4862 16796 58786 208012 742900 2674440 9694845