Nonnegative walks of length n on the x-axis starting at the origin using steps {1,0,-1} and visiting no point more than twice.

A212586

Nonnegative walks of length n on the x-axis starting at the origin using steps {1,0,-1} and visiting no point more than twice.

Terms

    a(0) =1a(1) =2a(2) =6a(3) =13a(4) =29a(5) =60a(6) =128a(7) =269a(8) =569a(9) =1198a(10) =2526a(11) =5321a(12) =11213a(13) =23624a(14) =49776a(15) =104873a(16) =220961a(17) =465546a(18) =980870a(19) =2066613a(20) =4354189a(21) =9173924a(22) =19328720a(23) =40724053a(24) =85802297a(25) =180778518a(26) =380885758a(27) =802495569a(28) =1690793437a(29) =3562365392

External references