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A230554 Number of involutions avoiding the pattern 1324. 0
1, 1, 2, 4, 9, 21, 51, 126, 321, 820, 2160, 5654, 15272, 40758, 112280, 304471, 852164, 2341980, 6640755, 18460066, 52915999 (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 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

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Last modified October 17 14:56 EDT 2018. Contains 316282 sequences. (Running on oeis4.)