a(n) = b(n) + b(n+1) + 2, where b() = A000930().

Terms

a(0) =4a(1) =4a(2) =5a(3) =7a(4) =9a(5) =12a(6) =17a(7) =24a(8) =34a(9) =49a(10) =71a(11) =103a(12) =150a(13) =219a(14) =320a(15) =468a(16) =685a(17) =1003a(18) =1469a(19) =2152a(20) =3153a(21) =4620a(22) =6770a(23) =9921a(24) =14539a(25) =21307a(26) =31226a(27) =45763a(28) =67068a(29) =98292