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A230551
Number of involutions avoiding the pattern 2431.
6
1, 2, 4, 10, 24, 62, 154, 396, 992, 2536, 6376, 16238, 40914, 103954, 262298, 665478, 1680726, 4260262, 10766470, 27274444
OFFSET
1,2
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 26, only 35142 and 52431 contain the pattern 2431, so a(5) = 24.
KEYWORD
nonn,more
AUTHOR
Cheyne Homberger, Oct 23 2013
STATUS
approved