A230551 Number of involutions avoiding the pattern 2431.

1, 2, 4, 10, 24, 62, 154, 396, 992, 2536, 6376, 16238, 40914, 103954, 262298, 665478, 1680726, 4260262, 10766470, 27274444

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: A055919 A006575 A307900 * A246566 A230553 A138175

Adjacent sequences: A230548 A230549 A230550 * A230552 A230553 A230554

Keyword

nonn

Author

Cheyne Homberger, Oct 23 2013

Status

approved