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

3,2

Links

Table of n, a(n) for n=3..29.

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

Crossrefs

Sequence in context: A372015 A026110 A056327 * A014532 A094705 A280786

Adjacent sequences: A026325 A026326 A026327 * A026329 A026330 A026331

Keyword

nonn

Author

Clark Kimberling

Status

approved