%I A002718 M4559 N1941
%S A002718 1,8,80,1088,19232,424400,11361786,361058000,13386003873,570886397340,
%T A002718 27681861184474,1511143062540976,92091641176725504,6219762391554815200,
%U A002718 462595509951068027741,37676170944802047077248
%N A002718 Number of bicoverings of an n-set.
%D A002718 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A002718 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A002718 L. Comtet, Birecouvrements et birevetements d'un ensemble fini. Studia 
               Sci. Math. Hungar. 3 1968 137-152.
%D A002718 L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 303, #40.
%D A002718 I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, John Wiley 
               and Sons, N.Y., 1983.
%F A002718 E.g.f. for k-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).
%Y A002718 Cf. A020554, A002719, A003462, A059945-A059951. Row sums of A059443.
%Y A002718 Sequence in context: A051580 A060375 A097815 this_sequence A057707 A145606 
               A002072
%Y A002718 Adjacent sequences: A002715 A002716 A002717 this_sequence A002719 A002720 
               A002721
%K A002718 nonn,nice,easy
%O A002718 2,2
%A A002718 N. J. A. Sloane (njas(AT)research.att.com).
%E A002718 More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Feb 18 2001