a(n) = 4*a(n-1) - a(n-2) + 3 with a(0)=1, a(1)=7.

Terms

a(0) =1a(1) =7a(2) =30a(3) =116a(4) =437a(5) =1635a(6) =6106a(7) =22792a(8) =85065a(9) =317471a(10) =1184822a(11) =4421820a(12) =16502461a(13) =61588027a(14) =229849650a(15) =857810576a(16) =3201392657a(17) =11947760055a(18) =44589647566a(19) =166410830212a(20) =621053673285