61

This number is a prime.

The sum of the lowest digit in each of the powers of two (2 + 4 + 8 + 1 + 2 + 4 + 1 + 2 + 1 + 0 + 0 + 0 + 1 + 1 + 2 + 3 + 0 ...) is 61 unless there are some large power of two that has no zero. [Gaydos]