a(n) = (2 cos(Pi/15))^n + (2 cos(7 Pi/15))^n + (2 cos(11 Pi/15))^n + (2 cos(13 Pi/15))^n.

Terms

a(0) =4a(1) =-1a(2) =9a(3) =-1a(4) =29a(5) =4a(6) =99a(7) =34a(8) =349a(9) =179a(10) =1254a(11) =824a(12) =4559a(13) =3574a(14) =16704a(15) =15004a(16) =61549a(17) =61709a(18) =227799a(19) =250229a(20) =846254a(21) =1004149a(22) =3153984a(23) =3997399a(24) =11788879a(25) =15812504a(26) =44178624a(27) =62229509a(28) =165946124a(29) =243873904