%I A026269
%S A026269 1,2,4,10,25,64,166,436,1157,3098,8360,22714,62086,170614,471096,1306374,
%T A026269 3636708,10159590,28473132,80032638,225562929,637301652,1804751718,
%U A026269 5121677512,14563448593,41487279622,118389089432,338381552294,968627180975
%N 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.
%F A026269 G.f.: 4z^2(1-z^2)/[1-z+sqrt(1-2z-3z^2)]^2.
%Y A026269 First differences of A102071.
%Y A026269 Sequence in context: A089928 A036887 A151536 this_sequence A000645 A005958 
               A166516
%Y A026269 Adjacent sequences: A026266 A026267 A026268 this_sequence A026270 A026271 
               A026272
%K A026269 nonn
%O A026269 2,2
%A A026269 Clark Kimberling (ck6(AT)evansville.edu)
%E A026269 More terms from R. Stephan, Dec 30 2004