Question

If there is 1 child, there can be 0 interactions.
If there are 2 children, there can be 3 interactions.
If there are 3 children, there can be 9 interactions.
If there are 4 children, there can be 18 interactions.

How many interactions will there be for 9 children?

135

84

93

108
How would I solve this?

Answer 1

is it \(a_n=a_{n-1}+3(n-1)\)?

Answer 2

Ok so would An =9 and n =3?

Answer 3

oh never mind I got it. Thank you so much :)