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2, 10, 114, 1322, 16428, 214660, 2897424, 40046134, 563527294, 8042361426, 116083167058, 1691193906828, 24830916046462, 366990100477712, 5454733737618820, 81475220265330158, 1222209564554562110, 18404140554678144630, 278069131820486935046, 4214088001120913287256, 64037903464421065585244
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listen;
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internal format)
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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S[0, 0] = 1; S[0, _] = 0; S[n_, k_] /; k < 0 || k > Binomial[n + 1, 2] = 0; S[n_, k_] := S[n, k] = S[n - 1, k] + S[n - 1, k - n];
b[n_] := 2 Sum[Sum[k2 = (n^2 - n)/4 - (n - i - 1) - k1; S[n - i - 2, k1]* S[i - 1, k2], {k1, 0, (n^2 - n)/4 - (n - i - 1)}] + Sum[k2 = (n^2 - n)/4; S[Floor[(n - 2)/2], k1]*S[Floor[(n - 2)/2], k2], {k1, 0, (n^2 - n)/4}], {i, 1, Floor[(n - 1)/2]}];
a[n_] := b[4n];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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