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%I #13 Oct 28 2013 13:29:49
%S 1,2,4,10,25,66,170,441,1124,2870,7273,18477,46825,118917,301734,
%T 766525,1946293,4944614,12557685
%N Number of involutions avoiding the pattern 2341.
%H Miklós Bóna, Cheyne Homberger, Jay Pantone, and Vince Vatter, <a href="http://arxiv.org/abs/1310.7003">Pattern-avoiding involutions: exact and asymptotic enumeration</a>, arxiv:1310.7003, 2013.
%e Of the 26 involutions of length 5, only 52341 contains the pattern 2341, so a(5) = 25.
%Y Cf. A001006, A121704, A230551-A230556.
%K nonn
%O 1,2
%A _Cheyne Homberger_, Oct 23 2013