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A027881
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a(i)=a(i-1)+a(j_1)*a(j_2) {where j_1+j_2=i-1, j_1 <= q j_2} + a(j_1)*a(j_2)*a(j_3) {where j_1+j_2+j_3=i-1, j_1 <= q j_2 <= q j_3} +...+ a(1)^{i-1}.
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0
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1, 1, 2, 4, 9, 20, 51, 121, 321, 826, 2186, 5789, 16114, 42449, 118281, 328425, 908933, 2510553, 7138324, 19869748
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OFFSET
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1,3
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COMMENTS
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At one time it was thought that this might be related to the Hopf algebra structure of perturbative Quantum Field Theory; this later proved not to be the case.
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LINKS
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Dirk Kreimer (kreimer(AT)dipmza.physik.Uni-Mainz.DE)
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STATUS
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approved
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