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 A059946 Number of 5-block bicoverings of an n-set. 3
 0, 0, 0, 25, 472, 6185, 70700, 759045, 7894992, 80736625, 817897300, 8241325565, 82783813112, 830046591465, 8313655213500, 83215436364085, 832626645756832, 8329096006484705, 83307920631515300, 833180902353754605, 8332418928963358152, 83327847634888960345 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 REFERENCES I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, John Wiley and Sons, N.Y., 1983. LINKS Index entries for linear recurrences with constant coefficients, signature (26,-255,1210,-2924,3384,-1440). 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). G.f.: x^4*(288*x^2-178*x+25) / ((x-1)*(2*x-1)*(3*x-1)*(4*x-1)*(6*x-1)*(10*x-1)). [Colin Barker, Jan 11 2013] MATHEMATICA With[{c=(1/5!)}, Table[c(10^n-5 6^n-10 4^n+20 3^n+30 2^n-60), {n, 20}]]  (* Harvey P. Dale, Apr 21 2011 *) 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 KEYWORD easy,nonn AUTHOR Vladeta Jovovic, Feb 14 2001 EXTENSIONS More terms from Colin Barker, Jan 11 2013 STATUS approved

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Last modified May 25 03:14 EDT 2019. Contains 323539 sequences. (Running on oeis4.)