**Given: **a_{n} = 2n + 1

Taking n = 1,

a_{1} = 2(1) + 1 = 2 + 1 = 3

Taking n = 2,

a_{2} = 2(2) + 1 = 4 + 1 = 5

Taking n = 3,

a_{3} = 2(3) + 1 = 6 + 1 = 7

Therefore the series is 3, 5, 7, …

So, a = 3, d = a_{2} – a_{1} = 5 – 3 = 2

Now, we have to find the sum of first n terms of the AP

⇒ S_{n} = 2n + n^{2}

**Hence, the sum of n terms is n**^{2} + 2n.