A230556 Number of involutions avoiding the pattern 4231.

1, 1, 2, 4, 9, 21, 51, 128, 327, 858, 2272, 6146, 16716, 46246, 128414, 361493, 1020506, 2913060, 8335405, 24067930, 69646035

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 53241, 42315, 52431, 52341, and 15342 contain the pattern 4231, so a(5) = 21.

Crossrefs

Cf. A000085, A001006, A121704, A230551-A230555.

Sequence in context: A001006 A086246 A247100 * A027057 A333105 A148071

Adjacent sequences: A230553 A230554 A230555 * A230557 A230558 A230559

Keyword

nonn,more

Author

Cheyne Homberger, Oct 23 2013

Status

approved