The method of sequence representation has never come

The method of sequence representation has never come

First of all, you know, sequence refers to a sequence of numbers, such as: 1,3,5,7,9,11,13,15. For convenience, let's record the first number as A1, the second number as A2,..., and the nth number as an. Now you can see the rule that the numbers after 15 are 17,19,21, but if we ask directly what the number 50 is (that is, the number represented by A50)

Some questions about sequence of numbers
1. Sn = 2n ^ 2 + 3N + 1, find an

Sn=2n^2+3n+1
S(n-1)=2(n-1)^2+3(n-1)+1
=2n^2-4n+2+3n-3+1
=2n^2+3n+1 - 4n-1
Sn-S(n-1)=2n^2+3n+1-2n^2-3n-1+4n+1
an=4n+1 (n＞1)
a1=s1=6,