What does the ** maths operator do in Python?

It is the power operator.

From the Python 3 docs:

The power operator has the same semantics as the built-in pow() function, when called with two arguments: it yields its left argument raised to the power of its right argument. The numeric arguments are first converted to a common type, and the result is of that type.

It is equivalent to 2¹⁶ = 65536, or pow(2, 16)