Find the nth term of this sequence:
5, 10, 15, 20, 25

The sequence advances by adding 5 to the previous number.
So the nth term is 5*n, given n>0 and goes to infinity.
Why?
Let's look at this: 
n=0 means first number in the sequence should be 0. This is wrong.
n=1  - next number is 5.
n=2 - next number is 10.