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) = 3. Also T(2n,n), where T is defined in A026022.

A026029

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) = 3. Also T(2n,n), where T is defined in A026022.

Terms

    a(0) =1a(1) =2a(2) =6a(3) =20a(4) =69a(5) =242a(6) =858a(7) =3068a(8) =11050a(9) =40052a(10) =145996a(11) =534888a(12) =1968685a(13) =7276050a(14) =26993490a(15) =100490220a(16) =375287550a(17) =1405622460a(18) =5278838100a(19) =19873977240a(20) =74994427170a(21) =283595947284

External references