linear algorithm to generate catalan numbers

catalan.py

def catalan():
  """Yields catalan numbers: 1 1 2 5 14 42 132..."""
  n = 0
  c = 1
  while 1:
    yield c
    n = n+1
    c = c * 2 * (2*n-1) / (n+1)

# print the first ten catalan numbers
from itertools import islice
for n, c in enumerate(islice(catalan(), 10)):
  print n, c