indexind combinations function - math problem

[Laur]

TS is talking about combinations (https://en.wikipedia.org/wiki/Combination).

And here is some theory how to solve his problem: https://en.wikipedia.org/wiki/Combinatorial_number_system.

OK.
It's probably good... anyway, I guessed it myself.

iC = i << 1 + j << 1 + ... // where << = shl

for any combinations of numbers 01234... ie from 0 not 1.

additionaly we don't use N.

Thancs.