a(n) = (3^(2*n) + 5^(2*n)) / 2.

A081421

a(n) = (3^(2*n) + 5^(2*n)) / 2.

Terms

    a(0) =1a(1) =17a(2) =353a(3) =8177a(4) =198593a(5) =4912337a(6) =122336033a(7) =3054149297a(8) =76315468673

External references