%I
%S 1,1,1,2,1,1,1,4,2,1,1,4,1,1,1,12,1,3,1,3,1,1,1,11,2,1,4,3,1,3,1,49,1,
%T 1,1,12,1,1,1,9,1,2,1,3,2,1,1,46,2,3,1,3,1,8,1,9,1,1,1,10,1,1,2,359,1,
%U 2,1,3,1,2,1,40,1,1,3,3,1,2,1,38,11,1,1
%N Number of groups of order 2n generated by involutions.
%C a(n) >= A104404(n). This can be proved using the characterization in A104404. Given an Abelian group G, the semidirect product G : <h>, where h^2 = 1 and hgh = g^(1) for any g in G, is generated by involutions. There is also a semidirect product Q8 : C2 generated by involutions. So an involutiongenerated group G : C2 exists for any finite group G that has all subgroups normal, and it can be shown that they are all nonisomorphic.
%H Eric M. Schmidt, <a href="/A235388/b235388.txt">Table of n, a(n) for n = 1..511</a>
%o (GAP)
%o IsInvolutionGenerated := G > Group(Filtered(G, g>g^2=Identity(G)))=G;
%o A235388 := function(n) local i, count; count := 0; for i in [1..NrSmallGroups(2*n)] do if IsInvolutionGenerated(SmallGroup(2*n, i)) then count := count + 1; fi; od; return count; end;
%K nonn
%O 1,4
%A _Eric M. Schmidt_, Jan 08 2014
