a(n) = (3^n - 1)*(3^n + 1)^2/32.

A152256

a(n) = (3^n - 1)*(3^n + 1)^2/32.

Terms

    a(0) =0a(1) =1a(2) =25a(3) =637a(4) =16810a(5) =450241a(6) =12123475a(7) =327035437a(8) =8827268020a(9) =238312027681

External references