Mersenne: Factoring 2^n+1 and 2^n-1

Hi, Ernst Mayer once mentioned to me that Prime95 needs twice the FFT size for 2^n+1 numbers (compared to 2^n+1 numbers). Does that mean that George is using the identity 2^(2n)-1 = (2^n+1)(2^n-1) ? I was wondering why ECM on 2^n+1 numbers took much longer than on 2^n-1 of the same size.. That

Re: Mersenne: Factoring 2^n+1 and 2^n-1

On 3 Nov 99, at 13:53, Alex Kruppa wrote: Ernst Mayer once mentioned to me that Prime95 needs twice the FFT size for 2^n+1 numbers (compared to 2^n+1 numbers). Does that mean that George is using the identity 2^(2n)-1 = (2^n+1)(2^n-1) ? I was wondering why ECM on 2^n+1 numbers took much