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A218383
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Number of nonempty subsets S of the powerset of a set of size n, that have the odd intersection property.
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2
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1, 6, 63, 2880, 1942305, 270460574370, 2342736463012620110115, 86772003564839307585762726826882765841700, 59169757600268575861444773339439520868680468342509442047838072019506515900898085
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OFFSET
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1,2
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COMMENTS
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A being a set, S belonging to P(P(A)) \ {{}} has the odd intersection property (oip) if there exists a set B (necessarily nonempty) included in A with |B∩S| odd for each s in S.
For instance for S={{1}, {1,2}} of A={1,2}, let's take B={1}, then |{1}∩{1}|=1 (odd) and |{1,2}∩{1})|=1 (odd), so S has oip.
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LINKS
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FORMULA
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a(n) = sum(i=0, n-1, ((-1)^(n-i-1))*(2^(2^i)-1)*prod(j=1,i,(2^(n-j+1)-1)/ (2^j-1)) * prod(j=1,n-i,2^j-1)).
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EXAMPLE
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For |A|=2, A = {1,2} and P(A) = {{}, {1}, {2}, {1,2}}
S can be
{{}, {1}, {2}, {1,2}}
{{}, {1}, {2}}
{{}, {1}, {1,2}}
{{}, {2}, {1,2}}
{{1}, {2}, {1,2}}
{{}, {1}}
{{}, {2}}
{{}, {1,2}}
{{1}, {1,2}} has oip, with B={1}
{{2}, {1,2}} has oip, with B={2}
{{1},{2}} has oip, with B={1, 2}
{{}}
{{1}} has oip, with B={1}
{{2}} has oip, with B={2}
{{1,2}} has oip, with B={1}
So we have 6 S with oip.
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PROG
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(PARI) d(m) = {for (n=1, m, v = sum(i=0, n-1, ((-1)^(n-i-1))*(2^(2^i)-1)* prod(j=1, i, (2^(n-j+1)-1)/(2^j-1))*prod(j=1, n-i, 2^j-1)); print1(v, ", "); ); }
(Maxima) A218383[n]:=sum(((-1)^(n-i-1))*(2^(2^i)-1)*prod((2^(n-j+1)-1)/(2^j-1), j, 1, i)* prod(2^j-1, j, 1, n-i), i, 0, n-1)$ makelist(A218383[n], n, 1, 9); /* Martin Ettl, Oct 30 2012 */
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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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