nth term of a series

[SuperTramp]

I'm struggling to find the nth term for this set of numbers

5, 24, 55, 98, 153, 220, 299

[IceMan]

5, 24, 55, 98, 153, 220, 299
1st differerence
19, 31, 43, 55, 67, 79
2nd Difference
12, 12, 12, 12, 12

must be a quadratic since th 2nd difference is the same
halve the 12 so if must be 6n + .....

by looking i got (3n+2)(2n-1)