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A172383
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a(0)=1, otherwise a(n) = Sum_{k=0..floor((n-1)/2)} binomial(n-k-1,k)*a(n-1-2*k).
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5
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1, 1, 1, 2, 4, 8, 19, 46, 118, 322, 903, 2653, 8053, 25194, 81387, 269667, 917529, 3197480, 11393821, 41497060, 154186653, 584151512, 2254240317, 8852998343, 35361762709, 143540660088, 591802631729, 2476701062087
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OFFSET
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0,4
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LINKS
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FORMULA
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G.f. A(x) satisfies: A(x) = 1 + (x/(1-x^2)) * A(x/(1-x^2)).
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EXAMPLE
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Eigensequence for number triangle
1;
1, 0;
0, 1, 0;
1, 0, 1, 0;
0, 2, 0, 1, 0;
1, 0, 3, 0, 1, 0;
0, 3, 0, 4, 0, 1, 0;
1, 0, 6, 0, 5, 0, 1, 0;
0, 4, 0, 10, 0, 6, 0, 1, 0;
1, 0, 10, 0, 15, 0, 7, 0, 1, 0;
0, 5, 0, 20, 0, 21, 0, 8, 0, 1, 0;
(augmented version of Riordan array (1/(1-x^2), x/(1-x^2)), A030528.
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MAPLE
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option remember;
if n = 0 then
1;
else
add(binomial(n-k-1, k)*procname(n-1-2*k), k=0..floor((n-1)/2)) ;
end if;
end proc:
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MATHEMATICA
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a[n_]:= If[n == 0, 1, Sum[Binomial[n-k-1, k]*a[n-2*k-1], {k, 0, Floor[(n-1)/2]}]]; Table[a[n], {n, 0, 30}] (* G. C. Greubel, Oct 07 2018 *)
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CROSSREFS
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KEYWORD
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easy,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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