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A026017 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) = 2, s(2n-1) = 5. Also a(n) = T(2n-1,n-2), where T is the array defined in A026009. 1
1, 5, 21, 83, 319, 1209, 4550, 17068, 63954, 239666, 898909, 3375825, 12697035, 47833905, 180510210, 682341000, 2583591150, 9798281910, 37218303330, 141585223494, 539395269462, 2057771255210, 7860697923436, 30065829471048, 115135255095140, 441410428339972 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

LINKS

Table of n, a(n) for n=2..27.

FORMULA

Expansion of (1+x^1*C^3)*C^4, where C = (1-(1-4*x)^(1/2))/(2*x) is g.f. for Catalan numbers, A000108.

Conjecture: (n+4)*a(n) +(-8*n-17)*a(n-1) +(19*n+1)*a(n-2) +6*(-2*n+5)*a(n-3)=0. - R. J. Mathar, Jun 20 2013

CROSSREFS

First differences of A003517.

Sequence in context: A217783 A221862 A216271 * A132310 A083319 A146041

Adjacent sequences:  A026014 A026015 A026016 * A026018 A026019 A026020

KEYWORD

nonn

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified November 21 11:32 EST 2018. Contains 317447 sequences. (Running on oeis4.)