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A007537
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Number of proper covers of an n-set.
(Formerly M5287)
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6
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0, 1, 45, 15913, 1073579193, 4611686005542975085, 85070591730234615801280047645054636261, 28948022309329048855892746252171976961956366698726387156269151989162886489297
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,3
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REFERENCES
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A. J. Macula, Covers of a finite set, Math. Mag., 67 (1994), 141-144.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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Table of n, a(n) for n=1..8.
Eric Weisstein's World of Mathematics, Proper Cover.
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MAPLE
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A007537 := proc(n) 1/2*sum((-1)^k*binomial(n, k)*2^(2^(n-k)), k=0..n)-2^(2^n)/4 end;
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MATHEMATICA
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Table[1/2 Sum[(-1)^k Binomial[n, k]2^(2^(n-k)), {k, 0, n}]-2^2^n/4, {n, 8}] (* From Harvey P. Dale, Oct 31 2011 *)
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CROSSREFS
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Cf. A003465.
Sequence in context: A201004 A171118 A199521 * A225991 A125113 A003739
Adjacent sequences: A007534 A007535 A007536 * A007538 A007539 A007540
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KEYWORD
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nonn,easy,nice
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AUTHOR
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N. J. A. Sloane, Simon Plouffe
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EXTENSIONS
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One more term from Emeric Deutsch, Aug 01 2005
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STATUS
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approved
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