a(n) = p^n + q^n, p = (1 + sqrt(21))/2, q = (1 - sqrt(21))/2.

Terms

a(0) =1a(1) =11a(2) =16a(3) =71a(4) =151a(5) =506a(6) =1261a(7) =3791a(8) =10096a(9) =29051a(10) =79531a(11) =224786a(12) =622441a(13) =1746371a(14) =4858576a(15) =13590431a(16) =37883311a(17) =105835466a(18) =295252021a(19) =824429351a(20) =2300689456a(21) =6422836211a(22) =17926283491a(23) =50040464546a(24) =139671882001a(25) =389874204731