a(n) = a(n-1) + 16*a(n-3) - 16*a(n-4), where a(0) = 1, a(1) = 4, a(2) = 8, a(3) = 12, a(4) = 76.

Terms

a(0) =1a(1) =4a(2) =8a(3) =12a(4) =76a(5) =140a(6) =204a(7) =1228a(8) =2252a(9) =3276a(10) =19660a(11) =36044a(12) =52428a(13) =314572a(14) =576716a(15) =838860a(16) =5033164a(17) =9227468a(18) =13421772a(19) =80530636a(20) =147639500a(21) =214748364a(22) =1288490188a(23) =2362232012a(24) =3435973836a(25) =20615843020a(26) =37795712204a(27) =54975581388a(28) =329853488332a(29) =604731395276