%I A059947
%S A059947 0,0,0,3,256,7255,149660,2681063,44659776,714287535,11154475420,
%T A059947 171673613023,2618246526896,39701554817015,599773397512380,
%U A059947 9038881598035383,136004367641775616,2044264589908169695
%N A059947 Number of 6-block bicoverings of an n-set.
%D A059947 I. P. Goulden and D. M.Jackson, Combinatorial Enumeration, John Wiley 
               and Sons, N.Y., 1983.
%F A059947 a(n)=(1/6!)*(15^n-6*10^n-15*7^n+30*6^n+60*4^n-50*3^n-180*2^n+240). 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).
%Y A059947 Cf. A002718, A059443, A003462, A059945, A059946, A059948-A059951.
%Y A059947 Sequence in context: A028918 A045824 A027860 this_sequence A051490 A003381 
               A058451
%Y A059947 Adjacent sequences: A059944 A059945 A059946 this_sequence A059948 A059949 
               A059950
%K A059947 easy,nonn
%O A059947 1,4
%A A059947 Vladeta Jovovic (vladeta(AT)eunet.rs), Feb 14 2001