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A230555 Number of involutions avoiding 3421. 1
1, 1, 2, 4, 10, 25, 66, 173, 460, 1218, 3240, 8602, 22878, 60794, 161668, 429752, 1142758, 3038173, 8078606, 21479469, 57113888 (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 45312 contains the pattern 3421, so a(5) = 25.

CROSSREFS

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

Sequence in context: A005958 A166516 A230552 * A189912 A268321 A195981

Adjacent sequences:  A230552 A230553 A230554 * A230556 A230557 A230558

KEYWORD

nonn

AUTHOR

Cheyne Homberger, Oct 23 2013

STATUS

approved

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Last modified October 19 02:23 EDT 2018. Contains 316327 sequences. (Running on oeis4.)