Primes

Three, five and seven are fine,
eleven and thirteen are sublime,
two is fun,
and thirty-one,
all of these numbers are prime!

Then there is one, all alone,
with no factors of its own,
not even prime,
but that's just fine,
for from one comes most math as its known.

A long time ago, just for fun,
in order to name a sum,
it had to be,
so you shall see,
the assumption of a unit one.