f(1) = 2; f(n) = f(n-1) + 7
f(2) = (2-1) + 7 = 1 + 7 =8
f(3) = (8-1) + 7 = 7 + 7 =14
f(4) = (14-1) + 7 = 13 + 7 =20
f(5) = (20-1) + 7 = 19 + 7 =26
and so on...so it's increase by 6
f(6) = 26 + 6 = 32
f(7) = 32 + 6 = 38
f(8) = 38 + 6 = 44
f(9) = 44 +6 = 50
f(10) = 50 + 6 = 56
