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%I M1892 N0746 #24 Jun 15 2015 18:31:13
%S 1,2,8,60,672,9953,184557,4142631,109813842,3373122370,118280690398,
%T 4678086540493,206625802351035,10107719377251109,543762148079927802,
%U 31975474310851749920,2044501883873268414092,141485408653554069693421
%N Number of even graphs with n edges.
%C a(n) appears to be [A060639(n) + 1] / 2. - _Ralf Stephan_, Aug 21 2004
%D D. G. Cantor, personal communication.
%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H Sean A. Irvine, <a href="/A001188/b001188.txt">Table of n, a(n) for n = 1..50</a>
%H E. N. Gilbert, <a href="http://dx.doi.org/10.4153/CJM-1956-046-2">Enumeration of labelled graphs</a>, Canad. J. Math., 8 (1956), 405-411.
%H E. N. Gilbert, <a href="/A001187/a001187.pdf">Enumeration of labelled graphs</a> (Annotated scanned copy)
%H R. W. Robinson, <a href="/A001187/a001187_1.pdf">First 50 terms of A1187 and A1188</a>
%p with(combinat);
%p g:=k->sum(stirling2(k,j),j=0..k)^2;
%p egf:=series((exp(x)-1+log(1+sum(g(k)*x^k/k!,k=1..infinity)))/2,x,20);
%p seq(n!*coeff(egf,x,n),n=1..20); # _Sean A. Irvine_, Mar 22 2012
%K nonn
%O 1,2
%A _N. J. A. Sloane_
%E More terms from _Sean A. Irvine_, Mar 21 2012
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