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A232466
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Number of dependent sets with largest element n.
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24
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0, 0, 1, 2, 4, 10, 20, 44, 93, 198, 414, 864, 1788, 3687, 7541, 15382, 31200, 63191, 127482, 256857, 516404, 1037104, 2080357, 4170283, 8354078, 16728270
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OFFSET
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1,4
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COMMENTS
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Let S be a set of positive integers. If S can be divided into two subsets which have equal sums, then S is said to be a dependent set.
Dependent sets are also called biquanimous sets. Biquanimous partitions are counted by A002219 and ranked by A357976. - Gus Wiseman, Apr 18 2024
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REFERENCES
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J. Bourgain, Λ_p-sets in analysis: results, problems and related aspects. Handbook of the geometry of Banach spaces, Vol. I,195-232, North-Holland, Amsterdam, 2001.
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LINKS
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EXAMPLE
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The a(1) = 0 through a(6) = 10 sets:
. . {1,2,3} {1,3,4} {1,4,5} {1,5,6}
{1,2,3,4} {2,3,5} {2,4,6}
{1,2,4,5} {1,2,3,6}
{2,3,4,5} {1,2,5,6}
{1,3,4,6}
{2,3,5,6}
{3,4,5,6}
{1,2,3,4,6}
{1,2,4,5,6}
{2,3,4,5,6}
(End)
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MAPLE
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b:= proc(n, i) option remember; `if`(i<1, `if`(n=0, {0}, {}),
`if`(i*(i+1)/2<n, {}, b(n, i-1) union map(p-> p+x^i,
b(n+i, i-1) union b(abs(n-i), i-1))))
end:
a:= n-> nops(b(n, n-1)):
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MATHEMATICA
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b[n_, i_] := b[n, i] = If[i<1, If[n == 0, {0}, {}], If[i*(i+1)/2 < n, {}, b[n, i-1] ~Union~ Map[Function[p, p+x^i], b[n+i, i-1] ~Union~ b[Abs[n-i], i-1]]]]; a[n_] := Length[b[n, n-1]]; Table[Print[a[n]]; a[n], {n, 1, 24}] (* Jean-François Alcover, Mar 04 2014, after Alois P. Heinz *)
biqQ[y_]:=MemberQ[Total/@Subsets[y], Total[y]/2];
Table[Length[Select[Subsets[Range[n]], MemberQ[#, n]&&biqQ[#]&]], {n, 10}] (* Gus Wiseman, Apr 18 2024 *)
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PROG
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(PARI) dep(S, k=0)=if(#S<2, return(if(#S, S[1], 0)==k)); my(T=S[1..#S-1]); dep(T, abs(k-S[#S]))||dep(T, k+S[#S])
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CROSSREFS
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A237258 (aerated) counts biquanimous strict partitions, ranks A357854.
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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