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A246019
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Number of palstars of length 2n over an alphabet of size 2.
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3
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1, 2, 6, 20, 66, 220, 732, 2440, 8134, 27124, 90452, 301656, 1006036, 3355224, 11190040, 37320144, 124467394, 415114844, 1384462172, 4617363016, 15399513116, 51359405064, 171290386824, 571276030192, 1905280915036, 6354363191688, 21192639534984, 70680248726256
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OFFSET
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0,2
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LINKS
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L. Bruce Richmond and J. Shallit, Counting the Palstars, Electronic Journal of Combinatorics, 21(3) (2014), #P3.25.
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PROG
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(PARI) \\ Richmond and Shallit, Section 2
U(k, size)= { local u; u= vector(size, x, 0); u[1]=1;
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]));
return(u); }
u = U(2, 101);
p = vector(length(u), x, 0); p[1]=1;
for(n=1, length(u)-1, p[n+1]=sum(i=1, n, u[i+1]*p[n-i+1]));
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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