A playground is being designed where children can interact with their friends in certain combinations. If there is 1 child, there can be 0 interactions. If there are 2 children, there can be 6 interactions. If there are 3 children, there can be 15 interactions. IF there are 4 children, there can be 27 interactions. How many interactions will there be for 7 children?

60
81***(My answer)
105
108

1 answer

I agree
http://www.wolframalpha.com/input/?i=pattern+%7B0,6,15,27%7D