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A026904
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Number of sets S of positive integers satisfying E(S)=n, where E = 2nd elementary symmetric function.
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2
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0, 1, 1, 1, 1, 2, 1, 2, 1, 2, 2, 3, 1, 3, 2, 2, 2, 3, 2, 4, 2, 2, 3, 4, 1, 4, 3, 3, 3, 4, 3, 4, 2, 3, 5, 5, 1, 4, 4, 4, 5, 4, 2, 6, 3, 3, 6, 5, 3, 5, 4, 4, 4, 6, 4, 8, 2, 2, 8, 6, 3, 5, 6, 4, 6, 6, 3, 7, 4, 5, 9, 6, 3, 6, 6, 6, 7, 4, 5, 9, 5, 3, 9, 9, 3, 7, 6, 4, 10, 8
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OFFSET
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1,6
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LINKS
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EXAMPLE
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a(2) = 2 counts {1,11}, {1,2,3}.
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MATHEMATICA
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a[n_] := Module[{r}, r[lim_, s1_, s2_] := r[lim, s1, s2] = If[s2 == n, 1, Sum[r[i, s1 + i, s2 + s1*i], {i, 1, Min[Quotient[n-s2, s1], lim - 1]}]]; Sum[r[i, i, 0], {i, 1, n}]];
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PROG
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(PARI) a(n)={my(recurse(lim, s1, s2)=if(s2==n, 1, sum(i=1, min((n-s2)\s1, lim-1), self()(i, s1+i, s2+s1*i)))); sum(i=1, n, recurse(i, i, 0))} \\ Andrew Howroyd, Dec 17 2018
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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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