a(n) = T(4,n), array T given by A048471.

Terms

a(0) =1a(1) =17a(2) =65a(3) =209a(4) =641a(5) =1937a(6) =5825a(7) =17489a(8) =52481a(9) =157457a(10) =472385a(11) =1417169a(12) =4251521a(13) =12754577a(14) =38263745a(15) =114791249a(16) =344373761a(17) =1033121297a(18) =3099363905a(19) =9298091729a(20) =27894275201a(21) =83682825617a(22) =251048476865a(23) =753145430609