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

Author

Cheyne Homberger, Oct 23 2013

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Cf. A001006, A121704, A230552-A230556.