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Search: id:A026269
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A026269 a(n) = number of (s(0), s(1), ..., s(n)) such that every s(i) is a nonnegative integer, s(0) = 0 = s(n), s(1) = 1, |s(i) - s(i-1)| <= 1 for i >= 2, |s(2) - s(1)| = 1, |s(3) - s(2)| = 1 if s(2) = 1. Also a(n) = T(n,n) and a(n) = Sum{T(k,k-1)}, k = 1,2,...,n, where T is array in A026268. +0
3
1, 2, 4, 10, 25, 64, 166, 436, 1157, 3098, 8360, 22714, 62086, 170614, 471096, 1306374, 3636708, 10159590, 28473132, 80032638, 225562929, 637301652, 1804751718, 5121677512, 14563448593, 41487279622, 118389089432, 338381552294, 968627180975 (list; graph; listen)
OFFSET

2,2

FORMULA

G.f.: 4z^2(1-z^2)/[1-z+sqrt(1-2z-3z^2)]^2.

CROSSREFS

First differences of A102071.

Sequence in context: A089928 A036887 A151536 this_sequence A000645 A005958 A166516

Adjacent sequences: A026266 A026267 A026268 this_sequence A026270 A026271 A026272

KEYWORD

nonn

AUTHOR

Clark Kimberling (ck6(AT)evansville.edu)

EXTENSIONS

More terms from R. Stephan, Dec 30 2004

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Last modified November 24 23:16 EST 2009. Contains 167481 sequences.


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