Number of length n+2 0..3 arrays with at most one downstep in every n consecutive neighbor pairs.

Terms

a(0) =64a(1) =225a(2) =608a(3) =1408a(4) =2936a(5) =5664a(6) =10280a(7) =17754a(8) =29416a(9) =47047a(10) =72984a(11) =110240a(12) =162640a(13) =234974a(14) =333168a(15) =464474a(16) =637680a(17) =863341a(18) =1154032a(19) =1524624a(20) =1992584a(21) =2578300a(22) =3305432a(23) =4201290a(24) =5297240a(25) =6629139a(26) =8237800a(27) =10169488a(28) =12476448a(29) =15217466