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

Terms

a(0) =1a(1) =1a(2) =5a(3) =9a(4) =29a(5) =65a(6) =181a(7) =441a(8) =1165a(9) =2929a(10) =7589a(11) =19305a(12) =49661a(13) =126881a(14) =325525a(15) =833049a(16) =2135149a(17) =5467345a(18) =14007941a(19) =35877321a(20) =91909085a(21) =235418369a(22) =603054709a(23) =1544728185a(24) =3956947021a(25) =10135859761a(26) =25963647845a(27) =66507086889a(28) =170361678269