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A055152 Proper covers of an unlabeled n-set. 2
0, 1, 14, 956, 9331320, 6406603065901952, 16879085743296493569230716352778240, 717956902513121252476003434439730211883694285987816199468264943161704448 (list; graph; refs; listen; history; internal format)
OFFSET

1,3

LINKS

Eric Weisstein's World of Mathematics, Proper covers

FORMULA

a(n)=(A003180 (n)-2*A003180 (n-1))/4.

Apparently a(n)=A002857(n)-A000612(n-1). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 22 2007

CROSSREFS

See A007537 for labeled case. Cf. A055621.

Sequence in context: A159871 A115458 A199651 * A171183 A064729 A189304

Adjacent sequences:  A055149 A055150 A055151 * A055153 A055154 A055155

KEYWORD

easy,nonn

AUTHOR

Vladeta Jovovic (vladeta(AT)eunet.rs), Jun 14 2000

EXTENSIONS

More terms from David Wasserman (wasserma(AT)spawar.navy.mil), Mar 21 2002

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Last modified February 15 04:23 EST 2012. Contains 205694 sequences.