Hi, i'm trying to write a function to find all primes from 2 to N. My idea is : take the first number (2) try to find whether it's a multiple of one of all existing primes ([] at first) add 2 to the list of primes take the following number (3) find if multiple of existing primes ([2]) add 3 to the list of primes take the following number (4) find if multiple of existing primes ([2, 3]) do not add 4 to the list of primes ... take the following number (8) find if multiple of existing primes ([2, 3, 5, 7]) do not add 8 to the list of primes take the following number (9) find if multiple of existing primes ([2, 3, 5, 7]) do not add 9 to the list of primes (multiple of 3) and so on... So, i would like a function like : f (x : xs) = g x : f xs g would return x if x is prime, [] otherwise But g would use the preceding value of f (list of primes before the calculation for x) that is a result of g itself. f needs g that needs f : what's wrong with my mind ? Perhaps i am still under control of imperative programming ? Thanks for your help, Didier.