a(n) = number of (s(0), s(1), ..., s(2n)) such that s(i) is a nonnegative integer and |s(i) - s(i-1)| = 1 for i = 1,2,...,n, s(0) = 3, s(2n) = 7. Also a(n) = T(2n,n-2), where T is defined in A026022.

A026031

a(n) = number of (s(0), s(1), ..., s(2n)) such that s(i) is a nonnegative integer and |s(i) - s(i-1)| = 1 for i = 1,2,...,n, s(0) = 3, s(2n) = 7. Also a(n) = T(2n,n-2), where T is defined in A026022.

Terms

    a(0) =1a(1) =6a(2) =28a(3) =120a(4) =494a(5) =1988a(6) =7888a(7) =31008a(8) =121125a(9) =471086a(10) =1826660a(11) =7068360a(12) =27313650a(13) =105452700a(14) =406923360a(15) =1569869760a(16) =6056194410a(17) =23366193084a(18) =90173331960a(19) =348102883184

External references