Which of the following is proposition P(5) for the sequence of propositions
for all positive integers n?

13+33 + 53 + …+(2n−1)3 = n2(2n2−1)

Sorry - I don't undersand your question. It looks like your trying to write a sequence, but the terms 13, 33, 53 etc are not equivalent to (2n-1)3. Also, on the right hand side is that meant to be

n^2(2n^2 - 1)

?