a(n+2) = 5*a(n+1) - 2*a(n), with a(0) = 1, a(1) = 4.

Terms

a(0) =1a(1) =4a(2) =18a(3) =82a(4) =374a(5) =1706a(6) =7782a(7) =35498a(8) =161926a(9) =738634a(10) =3369318a(11) =15369322a(12) =70107974a(13) =319801226a(14) =1458790182a(15) =6654348458a(16) =30354161926a(17) =138462112714a(18) =631602239718