a(0) = 5, a(1) = 5, and a(n) = 4*a(n-1) - a(n-2) - 4 for n >= 2.

Terms

a(0) =5a(1) =5a(2) =11a(3) =35a(4) =125a(5) =461a(6) =1715a(7) =6395a(8) =23861a(9) =89045a(10) =332315a(11) =1240211a(12) =4628525a(13) =17273885a(14) =64467011a(15) =240594155a(16) =897909605a(17) =3351044261a(18) =12506267435a(19) =46674025475a(20) =174189834461a(21) =650085312365