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A230555
Number of involutions avoiding 3421.
6
1, 1, 2, 4, 10, 25, 66, 173, 460, 1218, 3240, 8602, 22878, 60794, 161668, 429752, 1142758, 3038173, 8078606, 21479469, 57113888
OFFSET
0,3
LINKS
Miklós Bóna, Cheyne Homberger, Jay Pantone, and Vince Vatter, Pattern-avoiding involutions: exact and asymptotic enumeration, arxiv:1310.7003 [math.CO], 2013-2014.
EXAMPLE
Of the 26 involutions of length 5, only 45312 contains the pattern 3421, so a(5) = 25.
KEYWORD
nonn,more
AUTHOR
Cheyne Homberger, Oct 23 2013
STATUS
approved