a(n) = 4*a(n-1) - a(n-2) with a(0) = 4 and a(1) = 11.

Terms

a(0) =4a(1) =11a(2) =40a(3) =149a(4) =556a(5) =2075a(6) =7744a(7) =28901a(8) =107860a(9) =402539a(10) =1502296a(11) =5606645a(12) =20924284a(13) =78090491a(14) =291437680a(15) =1087660229a(16) =4059203236a(17) =15149152715a(18) =56537407624a(19) =211000477781a(20) =787464503500