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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
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
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
KEYWORD
nonn
STATUS
approved