the sum of 3 consecutive natural numbers, the first of which is n

the sum of 3 consecutive natural numbers, the first of which is n

Natural numbers are counting numbers, so we the following expression:
n + (n + 1) + (n + 2)

Combine n terms and constants:
(n + n + n) + (1 + 2)
3n + 3
Also expressed as 3(n + 1)