a(n) = s(n+3)/4, where s is A024949.

Terms

a(0) =1a(1) =1a(2) =5a(3) =9a(4) =13a(5) =33a(6) =73a(7) =145a(8) =313a(9) =657a(10) =1693a(11) =3705a(12) =8101a(13) =18753a(14) =45777a(15) =105857a(16) =238481a(17) =556257a(18) =1358901a(19) =3192585a(20) =7386269a(21) =17475041a(22) =42632153a(23) =101388497a(24) =238670857a(25) =566984561a(26) =1396385741a(27) =3345556153a(28) =7948311797a(29) =19091588993