a(n) = ((7 + sqrt(7))^n - (7 - sqrt(7))^n)^2/28.

A145020

a(n) = ((7 + sqrt(7))^n - (7 - sqrt(7))^n)^2/28.

Terms

    a(0) =1a(1) =196a(2) =23716a(3) =2458624a(4) =239754256a(5) =22776846400

External references