Easy I think. You just have to do a binary AND of the number n with (n – 1). If the result is 0, then n is a power of 2.

For example, 16 is 10000 in binary, 16-1=15 is 01111. And, of course, 10000 AND 01111 is 0 which indicates that 16 is a power of two.

Another example: if n is 12 (not a power of two), it is 1100. 11 is 1011. Anding both gives 1000 which is not 0 hence 12 is not a power of 2.