# Thread: Cannot find a formula for sum

1. ## Cannot find a formula for sum

I have a the following expression
0 + 5 + 14 + 33 + 56 + 85 + 120 = 313
I tried to find the pattern between these numbers to find a formula for the sum. I used subtraction and tried to find GCD but no luck. Can you please help me?

2. a_n= n^4/((1-n)^2*(1-n^6)) I think this is the sequence formula... I can't find formula for the sum yet...

3. I found this sequence 0,5,16,33,56,85,120,161,208,261,320 in the example section of id:A113103 - OEIS Search Results . I'm pretty sure it's the correct sequence (we have 14 instead of 16 tho).