a(n) = 2*a(n-1) + 6*a(n-2) for n >= 2, a(0) = 1, a(1) = 5.

Terms

a(0) =1a(1) =5a(2) =16a(3) =62a(4) =220a(5) =812a(6) =2944a(7) =10760a(8) =39184a(9) =142928a(10) =520960a(11) =1899488a(12) =6924736a(13) =25246400a(14) =92041216a(15) =335560832a(16) =1223368960a(17) =4460102912a(18) =16260419584a(19) =59281456640a(20) =216125430784a(21) =787939601408