divides d n = rem n d == 0

ld n = ldf 2 n

ldf k n
	| divides k n 	= k
	| k ^ 2 > n 	= n
	| otherwise		= ldf (k+1) n

factors n	
	| n < 1 = []
	| n == 1 = []
	| otherwise = p : factors (div n p) where p = ld n