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%I #18 Jul 25 2017 02:41:25
%S 1,2,6,20,66,220,732,2440,8134,27124,90452,301656,1006036,3355224,
%T 11190040,37320144,124467394,415114844,1384462172,4617363016,
%U 15399513116,51359405064,171290386824,571276030192,1905280915036,6354363191688,21192639534984,70680248726256
%N Number of palstars of length 2n over an alphabet of size 2.
%H Lars Blomberg, <a href="/A246019/b246019.txt">Table of n, a(n) for n = 0..100</a>
%H L. Bruce Richmond and J. Shallit, <a href="http://www.combinatorics.org/ojs/index.php/eljc/article/view/v21i3p25">Counting the Palstars</a>, Electronic Journal of Combinatorics, 21(3) (2014), #P3.25.
%o (PARI) \\ Richmond and Shallit, Section 2
%o U(k,size)= { local u; u= vector(size,x,0); u[1]=1;
%o for (i = 1,length(u)-1,if(i%2==1, u[i+1]=k*u[i], u[i+1]=k*u[i]-u[i\2+1]));
%o return(u); }
%o u = U(2,101);
%o p = vector(length(u),x,0); p[1]=1;
%o for(n=1,length(u)-1,p[n+1]=sum(i=1,n,u[i+1]*p[n-i+1]));
%o p \\ _Lars Blomberg_, Jul 25 2017
%Y Cf. A246020, A246021.
%K nonn
%O 0,2
%A _N. J. A. Sloane_, Aug 13 2014
%E Typo in name fixed by _Jeffrey Shallit_, Aug 14 2014
%E a(11)-a(18) from _Lars Blomberg_, Jul 25 2017
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