- #1
YASuperhero
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Homework Statement
I'm trying to find out the equation for how to find out where a number falls in a sequence.
An example sequence would be 3, 9, 18, 30, 45, 63, 84, 108, 135, 165...
108 is the 8th number in that sequence.
Homework Equations
If I use the equation (xn+xn^2)/2
(x = 3 & n = 8)
I'll get 108.
What I need is to use the 108 and 3 and get 8.
What's the equation?
Thanks!
The Attempt at a Solution
I don't know :(