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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 Andrew Howroyd, Table of n, a(n) for n = 1..200 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 *) PROG (PARI) a(n) = {(1/5!)*(10^n - 5*6^n - 10*4^n + 20*3^n + 30*2^n - 60)} \\ Andrew Howroyd, Jan 29 2020 CROSSREFS Column k=5 of A059443. Cf. A002718. 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 December 7 19:20 EST 2021. Contains 349585 sequences. (Running on oeis4.)