Well I'm sure it looks trivial to you. But the joys of math often aren't in the difficulty but the discovery. Would your prefer it not have been stated at all, or did you just want to let us know you understood it.
As well, i think the 2k+1 thing is drastically more trivial and not at all equivalent being that all you need to know for 2k+1 is that 2k+1=odd. 4k and especially 6k take a larger generalization and different analytical method and often aren't included in the definition of the primes we learn like 2k+1 (odd) is.
As well, i think the 2k+1 thing is drastically more trivial and not at all equivalent being that all you need to know for 2k+1 is that 2k+1=odd. 4k and especially 6k take a larger generalization and different analytical method and often aren't included in the definition of the primes we learn like 2k+1 (odd) is.