Math pow alternative in java

Question

I have a need to sum up power of 2 from any digit x to 0. If x=6,desired sum is 2pow6+2pow5+.....1. While I can always write a algorithm to wind down to 0 using Math.pow - this function seems notorious performance-wise in a loop. Would appreciate if someone could help achieving the same using shift binary operators - I hear they are much more efficient than pow.

Answer 1

2^n + 2^(n-1) + 2^(n-2) + ... + 2 + 1 = (2^(n+1) - 1) = ((1 << (n+1)) - 1)