Hi Penny,

If n is a positive integer then the notation n! (n factorial) is used to designate n × (n-2) × (n-3) × … × 2 × 1, so for example 3! = 3 × 2 × 1 = 6. This definition is extended to the case than n = 0 by defining 0! = 1.

I am not sure if the sequence is to start with n = 1 or n = 0 but I expect it's with n = 1. Thus the first five terms will come from n = 1, 2, 3, 4 and 5.

n = 1: 2 × 1! - 1 = 2 × 1 - 1 = 1
n = 2: 2 × 2! - 1 = 2 × 2 - 1 = 3
n = 3: 2 × 3! - 1 = 2 × 6 - 1 = 11
n = 4:
n = 5:

I hope this helps,
Penny