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A059949 Number of 8-block bicoverings of an n-set. 4
0, 0, 0, 0, 0, 535, 51640, 2771685, 114713760, 4127125695, 136631722920, 4292250804985, 130278290187760, 3863262740532195, 112733098867629240, 3252644718804860925, 93093809127731630400, 2649006256251644780935 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

REFERENCES

I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, John Wiley and Sons, N.Y., 1983.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..100

FORMULA

a(n)=(1/8!)*(28^n-8*21^n-28*16^n+56*15^n+168*11^n-224*10^n+210*8^n-840*7^n+700*6^n-840*5^n+1925*4^n+1064*3^n-5460*2^n+4368). E.g.f. for m-block bicoverings of an n-set is exp(-x-1/2*x^2*(exp(y)-1))*Sum_{i=0..inf} x^i/i!*exp(binomial(i, 2)*y).

G.f.: -5*x^6*(3390266880*x^8 -3368778336*x^7 +1334596314*x^6 -268312855*x^5 +27919999*x^4 -1171492*x^3 -29534*x^2 +4331*x -107) / ((x -1)*(2*x -1)*(3*x- 1)*(4*x -1)*(5*x -1)*(6*x -1)*(7*x -1)*(8*x -1)*(10*x -1)*(11*x -1)*(15*x -1)*(16*x -1)*(21*x -1)*(28*x -1)). - Colin Barker, Jul 08 2013

CROSSREFS

Cf. A002718, A059443, A003462, A059945-A059948, A059950-A059951.

Sequence in context: A252536 A067723 A252275 * A256088 A250709 A077076

Adjacent sequences:  A059946 A059947 A059948 * A059950 A059951 A059952

KEYWORD

easy,nonn

AUTHOR

Vladeta Jovovic, Feb 14 2001

STATUS

approved

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Last modified November 18 21:04 EST 2018. Contains 317331 sequences. (Running on oeis4.)