Number of length n+2 0..2 arrays with at most one downstep in every n consecutive neighbor pairs.

Terms

a(0) =27a(1) =75a(2) =168a(3) =331a(4) =597a(5) =1008a(6) =1616a(7) =2484a(8) =3687a(9) =5313a(10) =7464a(11) =10257a(12) =13825a(13) =18318a(14) =23904a(15) =30770a(16) =39123a(17) =49191a(18) =61224a(19) =75495a(20) =92301a(21) =111964a(22) =134832a(23) =161280a(24) =191711a(25) =226557a(26) =266280a(27) =311373a(28) =362361a(29) =419802