Is {1, 3, 6, 10, 15, ...} a subsequence of the natural numbers and, if so, what function composed with the natural numbers gives this subsequence? Thanks.
I am not sure how to make this work with what I have. I have the composition of f and g = [n(n+1)]/2 = {1, 3, 6, 10, 15, ...}. I know that f = {1, 2, 3, 4, ...}. I need to find g.