Number of double nodes (exactly two nodes on that level) for all Motzkin paths of length n.

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =6a(5) =14a(6) =32a(7) =74a(8) =180a(9) =457a(10) =1195a(11) =3177a(12) =8526a(13) =23018a(14) =62441a(15) =170153a(16) =465791a(17) =1280956a(18) =3538618a(19) =9817619a(20) =27348480a(21) =76467497a(22) =214532805a(23) =603732396a(24) =1703728554a(25) =4819990947a(26) =13667248631a(27) =38834528740a(28) =110556072877a(29) =315290709729