A209230 Number of set partitions of [n] that avoid 1231 and 1121.

1, 1, 2, 5, 13, 34, 88, 226, 578, 1476, 3768, 9620, 24564, 62728, 160192, 409096, 1044744, 2668048, 6813600, 17400400, 44436688, 113481248, 289805440, 740097568, 1890041888, 4826739776, 12326402432

Offset

0,3

Links

Table of n, a(n) for n=0..26.

V. Jelinek, T. Mansour, M. Shattuck, On multiple pattern avoiding set partitions, Adv. Appl. Math. 50 (2) (2013) 292-326, Example 4.16 H_{1121} and example 4.17 L_{1121}.

Index entries for linear recurrences with constant coefficients, signature (4,-4,0,2).

Formula

G.f (1-x-x^2)*(1-x)^2/(1-4*x+4*x^2-2*x^4), correcting a sign in denominators of the publication.

Crossrefs

Sequence in context: A027931 A218481 A267905 * A103142 A112844 A027933

Adjacent sequences: A209227 A209228 A209229 * A209231 A209232 A209233

Keyword

nonn,easy

Author

R. J. Mathar, Jan 12 2013

Status

approved