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A007537 Number of proper covers of an n-set.
(Formerly M5287)
7
0, 1, 45, 15913, 1073579193, 4611686005542975085, 85070591730234615801280047645054636261, 28948022309329048855892746252171976961956366698726387156269151989162886489297 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
A. J. Macula, Covers of a finite set, Math. Mag., 67 (1994), 141-144.
Eric Weisstein's World of Mathematics, Proper Cover.
FORMULA
a(n) ~ 2^(2^n)/4. - Vaclav Kotesovec, Jul 02 2016
MAPLE
A007537 := proc(n) 1/2*sum((-1)^k*binomial(n, k)*2^(2^(n-k)), k=0..n)-2^(2^n)/4 end;
MATHEMATICA
Table[1/2 Sum[(-1)^k Binomial[n, k]2^(2^(n-k)), {k, 0, n}]-2^2^n/4, {n, 8}] (* Harvey P. Dale, Oct 31 2011 *)
CROSSREFS
Cf. A003465.
Sequence in context: A201004 A171118 A199521 * A287434 A225991 A125113
KEYWORD
nonn,easy,nice
AUTHOR
EXTENSIONS
One more term from Emeric Deutsch, Aug 01 2005
STATUS
approved

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Last modified March 19 04:58 EDT 2024. Contains 370952 sequences. (Running on oeis4.)