3 ms·
Not all 2^N - 1 are prime. For example, N=18 makes 2^N - 1 = 262143, which can also be written as 3^3 * 7 * 19 * 73 (not prime).
by aaronmdjones 2y ago
Not all 2^N - 1 are prime. For example, N=18 makes 2^N - 1 = 262143, which can also be written as 3^3 * 7 * 19 * 73 (not prime).
- stevefan1999 2y agoOh, right, all Mersenne number is in the form of 2^N -1, but Mersenne prime is Mersenne number plus being prime
- mort96 2y agoAnd we look for Mersenne primes, AFAIU, mainly because Mersenne numbers are more likely to be prime than other numbers, so it's easier to find big primes that way.
- School-Cotton 2y agoA lot simpler example is 2^4-1=5*3
- lupire 2y ago2^11-1 (prime power) for a less trivial example