superpollo wrote: > goal (from e.c.m.): evaluate > 1^2+2^2+3^2-4^2-5^2+6^2+7^2+8^2-9^2-10^2+...-2010^2, where each three > consecutive + must be followed by two - (^ meaning ** in this context) >>> from itertools import cycle, izip >>> sum(sign*i*i for sign, i in izip(cycle([1]*3+[-1]*2), range(1, 2011))) 536926141