math
posted by Shay .
How do you find the nth term in a sequence of numbers if the values are increasing then decreasing? Ex. 1: 2, 3: 10, 5: 18

There are probably more than one "correct" answer.
1: 2, 3: 10, 5: 18
I think of it as two separate series interleaved together, namely:
1, 3, 5, 7, 9....
and
2, 10, 18, 26, 34, ....
Your teacher has the final word.