Is the sum of the first n terms of 65438+0,2,3,4,5, ...

When n= 1, 1 ×2/2= 1.

When n=2, 2 ×3/2=3.

When n=3, 3 ×4/2=6.

When n=4, 4×5/2= 10.

When n=5, 5×6/2= 15,

When n=6, 6×7/2=2 1.

You can also look at 1 in this way.

3= 1+2

6= 1+2+3

10= 1+2+3+4

15= 1+2+3+4+5

...