One term in the series 5, 9, 17, 33, 65, 128 does not fit the rule the others follow. Which term is out of place?

Each term should be double the one before it less one: $5\times 2-1=9,9\times 2-1=17,17\times 2-1=33,33\times 2-1=65$. The last term should therefore be $65\times 2-1=129$, not 128. Every earlier term obeys the rule exactly, so 9, 33 and 65 are all in place; the fault lies at the end of the series.