Counting combinations

If I have a form like:
2^k - 1, then that number  is all the bits set from the k-1 bit to the first bit, say N bits.

How many combinations can I count with those bits?

2^N  * 2^N-1 * ... *2^1, or by adding up the bits 2^{1/2*N*(N+1)}

So that become the SNR in a minimum redundancy counter. In counting [primes, the k jumps by two, k: k+1,k+2, and the middle bits give up combinations to maintain symmetry.  So, it seems, my system might make sense, I am using counters to their maximum utility, not computing the prime but counting them. I compute primes later as in the previous post.