Sequence relating to the benzene ring.

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =14a(5) =30a(6) =83a(7) =255a(8) =807a(9) =2482a(10) =7399a(11) =21518a(12) =61752a(13) =176385a(14) =504181a(15) =1445159a(16) =4153716a(17) =11960039a(18) =34463630a(19) =99316022a(20) =286133435a(21) =824112803a(22) =2373059251a(23) =6832536414a(24) =19671776119a(25) =56638681010a(26) =163078362040a(27) =469559902129