Number of length n+1 0..3 arrays with at most one downstep in every n consecutive neighbor pairs.

Terms

a(0) =16a(1) =60a(2) =190a(3) =512a(4) =1212a(5) =2592a(6) =5115a(7) =9460a(8) =16588a(9) =27820a(10) =44928a(11) =70240a(12) =106760a(13) =158304a(14) =229653a(15) =326724a(16) =456760a(17) =628540a(18) =852610a(19) =1141536a(20) =1510180a(21) =1976000a(22) =2559375a(23) =3283956a(24) =4177044a(25) =5269996a(26) =6598660a(27) =8203840a(28) =10131792a(29) =12434752