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A057668 Number of minimal 7-covers of a labeled n-set. 1
1, 988, 549102, 226064280, 76785889587, 22762819040676, 6092115565691584, 1505097773271664000, 348617485585838373333, 76564317282173987801964, 16080209472530744351164146, 3250906483045575317042337960, 635954979082842132795003641239 (list; graph; refs; listen; history; text; internal format)
OFFSET

7,2

LINKS

Table of n, a(n) for n=7..19.

Eric Weisstein's World of Mathematics, Minimal cover

FORMULA

a(n) = (1/7!) * (127^n - 7 * 126^n + 21 * 125^n - 35 * 124^n + 35 * 123^n - 21 * 122^n + 7 * 121^n - 120^n).

G.f.: x^7 / ((120*x-1)*(121*x-1)*(122*x-1)*(123*x-1)*(124*x-1)*(125*x-1)*(126*x-1)*(127*x-1)). - Colin Barker, Jul 11 2013

CROSSREFS

Cf. A000392, A003468, A016111, A046166-A046169, A005783-A005786, A055066 (unlabeled case).

Sequence in context: A235545 A232429 A232844 * A217719 A223156 A087702

Adjacent sequences:  A057665 A057666 A057667 * A057669 A057670 A057671

KEYWORD

easy,nonn

AUTHOR

Vladeta Jovovic, Oct 16 2000

EXTENSIONS

Additional term from Colin Barker, Jul 11 2013

STATUS

approved

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Last modified January 25 04:27 EST 2021. Contains 340416 sequences. (Running on oeis4.)