Number of closed walks of length n along the edges of a tetrahedron based at a vertex.

Terms

a(0) =1a(1) =0a(2) =3a(3) =6a(4) =21a(5) =60a(6) =183a(7) =546a(8) =1641a(9) =4920a(10) =14763a(11) =44286a(12) =132861a(13) =398580a(14) =1195743a(15) =3587226a(16) =10761681a(17) =32285040a(18) =96855123a(19) =290565366a(20) =871696101a(21) =2615088300a(22) =7845264903a(23) =23535794706a(24) =70607384121a(25) =211822152360a(26) =635466457083