a(n) = (5^(2*(n + 1)) - 1)/4.

A275766

a(n) = (5^(2*(n + 1)) - 1)/4.

Terms

    a(0) =156a(1) =3906a(2) =97656a(3) =2441406a(4) =61035156a(5) =1525878906a(6) =38146972656a(7) =953674316406

External references