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A230556 Number of involutions avoiding the pattern 4231. 6
1, 1, 2, 4, 9, 21, 51, 128, 327, 858, 2272, 6146, 16716, 46246, 128414, 361493, 1020506, 2913060, 8335405, 24067930, 69646035 (list; graph; refs; listen; history; text; internal format)
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 A148071 A000636

Adjacent sequences:  A230553 A230554 A230555 * A230557 A230558 A230559

KEYWORD

nonn

AUTHOR

Cheyne Homberger, Oct 23 2013

STATUS

approved

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Last modified February 18 17:08 EST 2018. Contains 299325 sequences. (Running on oeis4.)