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

Terms

a(0) =81a(1) =216a(2) =441a(3) =789a(4) =1302a(5) =2032a(6) =3042a(7) =4407a(8) =6215a(9) =8568a(10) =11583a(11) =15393a(12) =20148a(13) =26016a(14) =33184a(15) =41859a(16) =52269a(17) =64664a(18) =79317a(19) =96525a(20) =116610a(21) =139920a(22) =166830a(23) =197743a(24) =233091a(25) =273336a(26) =318971a(27) =370521a(28) =428544a(29) =493632