A026328 a(n) = number of (s(0), s(1), ..., s(n)) such that s(i) is a nonnegative integer and |s(i) - s(i-1)| <= 1 for i = 1,2,...,n, s(0) = 2, s(n) = 5. Also a(n) = T(n,n-3), where T is the array in A026323.

1, 4, 15, 50, 161, 504, 1553, 4730, 14289, 42900, 128193, 381654, 1132950, 3355392, 9918990, 29278012, 86316259, 254227980, 748200145, 2200619806, 6469372932, 19011518480, 55853259800, 164055406320, 481804384035, 1414857108756, 4154663090529

Offset: 3

Author

Clark Kimberling

Keywords

• nonn

Formula

Conjecture: -(n+9)*(n-3)*a(n) +(6*n^2+21*n-128)*a(n-1) +(-9*n^2-3*n+152)*a(n-2) -4*(n+4)*(n-1)*a(n-3) +12*(n-1)*(n-2)*a(n-4)=0. - R. J. Mathar, Jun 23 2013