The first 6 terms are 4, 12, 21, 31, 42 and 54
Step-by-step explanation:
⇒ f(1) = 4
⇒ f(2) = f(1) + (2+6) = 4 + 8 = 12
⇒ f(3) = f(2) + (3+6) = 12 + 9 = 21
⇒ f(4) = f(3) + (4+6) = 21 + 10 = 31
⇒ f(5) = f(4) + (5+6) = 31 + 11 = 42
⇒ f(6) = f(5) + (6+6) = 42 + 12 = 54