A230554 Number of involutions avoiding the pattern 1324.

1, 1, 2, 4, 9, 21, 51, 126, 321, 820, 2160, 5654, 15272, 40758, 112280, 304471, 852164, 2341980, 6640755, 18460066, 52915999

Offset

0,3

Links

Table of n, a(n) for n=0..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 5, only 21435, 13254, 13245, 14325, and 12435 contain the pattern 1324, so a(5) = 21.

Crossrefs

Cf. A000085, A001006, A121704, A230551-A230556.

Sequence in context: A257386 A048285 A051529 * A005207 A257519 A257387

Adjacent sequences: A230551 A230552 A230553 * A230555 A230556 A230557

Keyword

nonn

Author

Cheyne Homberger, Oct 23 2013

Status

approved