A026027 a(n) = number of (s(0), s(1), ..., s(2n-1)) 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-1) = 6. Also a(n) = T(2n-1,n-2), where T is defined in A026022.

1, 5, 21, 84, 329, 1274, 4900, 18768, 71706, 273581, 1043119, 3976700, 15163785, 57848910, 220830360, 843621600, 3225477150, 12342901410, 47274639594, 181230395304, 695384769002, 2670587146260, 10265249568536, 39491671919840

Offset

2,2

Links

Table of n, a(n) for n=2..25.

Formula

C(2n-1, n-2) - C(2n-1, n-6). G.f.: (1+x^2C^4)*C^5, where C=(1-sqrt(1-4x))/(2x). - Ralf Stephan, Jan 09 2005

Conjecture: (13*n+118)*(n+5)*a(n) +(13*n^2-969*n-3490)*a(n-1) +2*(-203*n^2+1080*n+758)*a(n-2) +4*(73*n-182)*(2*n-5)*a(n-3)=0. - R. J. Mathar, Jun 22 2013

Crossrefs

Sequence in context: A146585 A351363 A215008 * A002054 A289797 A246986

Adjacent sequences: A026024 A026025 A026026 * A026028 A026029 A026030

Keyword

nonn

Author

Clark Kimberling

Status

approved