1,4,15,64,325,?

This sequence appears to follow a pattern where each term is one less than a perfect square or a perfect cube.

1 is 2^0 - 1 4 is 2^2 - 1 15 is 2^4 - 1 64 is 4^3 - 1 325 is 6^3 - 1

Following this pattern, the next term should be one less than the next perfect square or cube. The next number in the sequence of squares and cubes is 8^3 or 512.

So, the next term in the sequence should be 512 - 1 = 511.

Therefore, the missing number in the sequence is 511.