Posted by **Cassie** on Tuesday, April 21, 2009 at 3:46pm.

Let a be the value of the function when n is 0. The number of the first row of differences is b, the first number of the next row is c, and so on. The formula for the nth number of the series is:

a + bn + cn(n-1)/2! + dn(n-l)(n-2)/3! and so on.

Find the formula for each pattern.

Here is the one I'm having trouble with:

6, 15, 24, 39, 60.

Please help if you can!

Thank you! :-)