1 is 3, 2 is 6, 3 is 10, 4 is 15 ask the nth number (formula) thank you! I'm in a hurry

1 is 3, 2 is 6, 3 is 10, 4 is 15 ask the nth number (formula) thank you! I'm in a hurry


A B
1 3
2 6
3 10
4 15
B1=(A1+2)*(A1+1)/2