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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..20.

Miklós Bóna, Cheyne Homberger, Jay Pantone, and Vince Vatter, Pattern-avoiding involutions: exact and asymptotic enumeration, arxiv:1310.7003, 2013.

EXAMPLE

Of the 26 involutions of length 26, only 35142 and 52431 contain the pattern 2431, so a(5) = 24.

CROSSREFS

Cf. A001006, A121704, A230552-A230556.

Sequence in context: A088354 A055919 A006575 * A246566 A230553 A138175

Adjacent sequences:  A230548 A230549 A230550 * A230552 A230553 A230554

KEYWORD

nonn

AUTHOR

Cheyne Homberger, Oct 23 2013

STATUS

approved

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Last modified October 23 16:15 EDT 2018. Contains 316529 sequences. (Running on oeis4.)