Test if given number is a Keith number
Python (78 75)

a=input()
n=map(int,`a`)
while a&gt;n[0]:n=n[1:]+[sum(n)]
print(a==n[0])&amp;(a&gt;9)


n=n[1:]+[sum(n)] does all the magic. It takes every item but the first item of n, sticks on the sum of n (with the first item), then sets that to n.

I wish you could call list on an integer and have the digits seperated.

Returns False on all inputs below 10. Can be 8 characters shorter if it returned True.