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A307789 Number of valid hook configurations of permutations of [n] that avoid the patterns 231 and 1243. 0
1, 1, 1, 2, 5, 13, 35, 96, 267, 750, 2123, 6046, 17303, 49721, 143365, 414584, 1201917, 3492117, 10165779, 29643870, 86574831, 253188111, 741365049, 2173243128, 6377181825, 18730782252, 55062586341, 161995031226, 476941691177, 1405155255055 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Essentially the same as A005773. - R. J. Mathar, May 06 2019

LINKS

Table of n, a(n) for n=0..29.

Colin Defant, Motzkin intervals and valid hook configurations, arXiv preprint arXiv:1904.10451 [math.CO], 2019.

FORMULA

G.f.: 1 + 2*x^2/(3*x - 1 + sqrt(1 - 2*x - 3*x^2)).

CROSSREFS

Cf. A005773.

Sequence in context: A085810 A235611 A005773 * A022855 A091190 A264228

Adjacent sequences:  A307786 A307787 A307788 * A307790 A307791 A307792

KEYWORD

nonn

AUTHOR

Colin Defant, Apr 28 2019

STATUS

approved

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Last modified October 15 00:14 EDT 2019. Contains 328025 sequences. (Running on oeis4.)