Walks with n steps on the x-axis using steps {1,0,-1} and visiting no point more than twice.

Terms

a(0) =1a(1) =3a(2) =8a(3) =18a(4) =34a(5) =64a(6) =118a(7) =214a(8) =382a(9) =678a(10) =1198a(11) =2112a(12) =3716a(13) =6532a(14) =11474a(15) =20148a(16) =35370a(17) =62084a(18) =108964a(19) =191234a(20) =335608a(21) =588968a(22) =1033584a(23) =1813832a(24) =3183072a(25) =5585922a(26) =9802630a(27) =17202438a(28) =30188196a(29) =52976614