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A059946
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Number of 5-block bicoverings of an n-set.
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2
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0, 0, 0, 25, 472, 6185, 70700, 759045, 7894992, 80736625, 817897300, 8241325565, 82783813112, 830046591465, 8313655213500, 83215436364085, 832626645756832, 8329096006484705, 83307920631515300, 833180902353754605
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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REFERENCES
| I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, John Wiley and Sons, N.Y., 1983.
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FORMULA
| a(n)=(1/5!)*(10^n-5*6^n-10*4^n+20*3^n+30*2^n-60). 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).
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MATHEMATICA
| With[{c=(1/5!)}, Table[c(10^n-5 6^n-10 4^n+20 3^n+30 2^n-60), {n, 20}]] (* From Harvey P. Dale, Apr 21 2011 *)
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CROSSREFS
| Cf. A002718, A059443, A003462, A059945, A059947-A059951.
Sequence in context: A056069 A089386 A014927 * A118445 A000497 A028341
Adjacent sequences: A059943 A059944 A059945 * A059947 A059948 A059949
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KEYWORD
| easy,nonn
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AUTHOR
| Vladeta Jovovic (vladeta(AT)eunet.rs), Feb 14 2001
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