Given that
f(n) = n^3 -1
when
n = 1
f(n) = 1^3 - 1
= 1 - 1
= 0
n = 2
f(n) = 2^3 - 1
= 8 - 1
= 7
n = 3
f(n) = 3^3 - 1
= 27 - 1
= 26
n = 4
f(n) = 4^3 - 1
= 64 - 1
= 63
