I'm having very unusual problems posting in the math forum. I am trying to write a program that would calculate phi, the CDF of the standard normal curve, in Python. I tried calculating the erf using a series to do it, as described by Wikipedia. But mine diverges, when it should approach 1. PHP: def erfterm(x, n): num = (-1.0)**n * x**(2*n+1) denum = fact(n) * (2*n+1) return num/denum def erf(x): #By Maclaurin series def term(n): num = (-1.0)**n * x**(2*n+1) denum = fact(n) * (2*n+1) return num/denum return sum([erfterm(x, i) for i in range(25)]) *(2 * sqrt(pi)) Something seems to be wrong with erfterm, because it's giving very large results. What gives? Is the equation at Wikipedia wrong? Or did I copy it wrong? Or is my computer wrong?