That is to say, A (S+ 1)-A (S) = 2+S, and s is counted from 1.
You can see it by listing more items:
A noun
-A(N- 1)=N+ 1
A(N- 1)-A(N-2)=N
...
Answer (2)
-A( 1)
=3
Add them all up to get a (n)-a (1) = 3+4+...+(n+1).
So A(N)=3+(N+4)(N- 1)/2.
Check the case where n is smaller again and find that there is no problem, so the answer is this.
Brainstorm, a person went out to play 10 Jin of wine at night, and met a friend on the way home. It happens that this friend is going to play win