We know that nth term of an A.P is given by,
an = a + (n – 1) d
Now equating it with the expression given we get,
2 n + 1 = a + (n – 1) d
2 n + 1 = a + nd – d
2 n + 1 = nd + (a – d)
Equating both sides we get,
d = 2 and a – d = 1
So we get,
a = 3 and d = 2.
So the first term of this sequence is 3, and the common difference is 2.