riddle - The circle of three

I'm the first, but also second

I'm rather odd, but also not

I am the circle of three

What am I?

Answer

You are:

2

I'm the first, but also second

The first prime, but also the second (depending on convention: 1 used to be regarded as prime).

I'm rather odd, but also not

2 is the oddest prime (it is even).

The circle of three

???