Nth Term query?

Question

Need help with modifying an nth term formula. i am using standard nth term formula for triangular sequence to show nth term for following
T S M (t = term, S = sets, M = moves)
1,2,1
2,3,3
3,4,6
4,5,10
I need to modify this formula to calculate different amounts of S (sets) - Any help??

Answer 1

Notice how the move is equal to half of the term times the sets.
M = (S * T) / 2

Or expressing it all using sets:
M = S (S - 1) / 2

If n is the term, then another equivalent way would be:
M = n(n + 1) / 2