Perfect Integer Problem

Atreides

You know the perfect integer formula 2^(n-1)x(2^n - 1) where (2^n - 1) is prime, seems to give me really messed up answers like if I put in 11 as the prime or 17, What am I doing wrong here. I'd really like to figure this how as I want to write a C++ program to calculate prime numbers and/or perfect integers, using this formula (there are longer ways to do it, and they work, but I'd also like to try this)

ecksor

You're looking for mersenne primes, along the lines of 3, 7, 31, 127 etc.

I.e, the number must be of the form 2^n-1 AND prime.

Atreides

is that where n is a whole number?

ecksor

Yeah. 2^2 - 1 = 3 which is prime, 2^3 - 1 = 7 which is prime, 2^5 - 1 = 31 which is prime, etc, and because they're all primes of that form they're mersenne primes.

This discusses the connection between mersenne primes and perfect numbers.
http://www.utm.edu/research/primes/mersenne/

Atreides

thank you, that makes writing this thing allot easier