%I A026945
%S A026945 1,2,9,51,323,2188,15511,113634,853467,6536382,50852019,400763223,
%T A026945 3192727797,25669818476,208023278209,1697385471211,13933569346707,
%U A026945 114988706524270,953467954114363,7939655757745265,66368199913921497
%N A026945 A bisection of the Motzkin numbers A001006.
%C A026945 a(n) = sum of the squares of numbers in row n of array T given by A026300.
%C A026945 Number of closed walks of length 2n on the one-way infinite ladder graph 
               starting from (and ending at) a node of degree 2. - Mitch Harris, 
               Mar 06 2004
%C A026945 a(n) = number of ways to connect 2n points labeled 1,2,...,2n in a line 
               with 0 or more noncrossing arcs. For example, with arcs separated 
               by dashes, a(2)=9 counts {} (no arcs), 12, 13, 14, 23, 24, 34, 12-34, 
               14-23. - David Callan (callan(AT)stat.wisc.edu), Sep 18 2007
%F A026945 a(n) = A005043(2n) + A005043(2n+1). - Ralf Stephan, Feb 06 2004
%F A026945 a(n)=sum{k=0..n, C(2n,2k)*C(k)}, C(n)=A000108(n); - Paul Barry (pbarry(AT)wit.ie), 
               Jul 11 2008
%p A026945 G:=(1-x-(1-2*x-3*x^2)^(1/2))/(2*x^2): GG:=series(G,x=0,60): 1, seq(coeff(GG,
               x^(2*n)),n=1..23);
%Y A026945 Cf. A001006, A099250.
%Y A026945 Sequence in context: A047069 A020087 A079836 this_sequence A009310 A091319 
               A003584
%Y A026945 Adjacent sequences: A026942 A026943 A026944 this_sequence A026946 A026947 
               A026948
%K A026945 nonn,easy
%O A026945 0,2
%A A026945 Clark Kimberling (ck6(AT)evansville.edu)
%E A026945 Entry revised by N. J. A. Sloane (njas(AT)research.att.com), Nov 16 2004
%E A026945 More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Nov 17 2004