A026329 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) = 6. Also a(n) = T(n,n-4), where T is the array in A026323.

1, 5, 21, 77, 266, 882, 2849, 9031, 28236, 87360, 268086, 817362, 2479008, 7486528, 22529250, 67598086, 202325585, 604317021, 1801836652, 5364359966, 15950297370, 47375004170, 140581490790, 416834841150, 1235113792185, 3657632434701

Offset

4,2

Links

Table of n, a(n) for n=4..29.

Formula

Conjecture: -(n+10)*(n-4)*a(n) +3*(2*n+15)*(n-4)*a(n-1) +3*(-3*n^2-n+68)*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: A271694 A245034 A126645 * A014533 A255453 A134770

Adjacent sequences: A026326 A026327 A026328 * A026330 A026331 A026332

Keyword

nonn

Author

Clark Kimberling

Status

approved