Hmm, it depends on what you're trying to show it is a multiple of. Here we wanted a multiple of 4, so I realised that because we have squares, we may as well use
2n, as when squared, that'll give us the factor of 4 we want.
However, using
2n and
2n+1 will result in larger coefficients, which given the nature of questions you're likely to get, will probably make the proofs come out a lot easier / nicer.