Question

1,3,7,13,21,31.的通项公式

Answer 1

3+4=7

7+6=3+4+6=13

13+8=3+4+6+8=21

21+10=3+4+6+8+10=31

……

an=3+4(n-1)+(n-1)(n-2)*2/2

=3+4n-4+n^2-3n+2

=n^2+n+1