A276720 Number of set partitions of [n] such that for each block b the smallest integer interval containing b has at most four elements.

1, 1, 2, 5, 15, 37, 87, 208, 515, 1271, 3112, 7594, 18578, 45510, 111464, 272839, 667809, 1634784, 4002217, 9797781, 23985131, 58715973, 143739040, 351879841, 861416293, 2108779100, 5162371032, 12637686756, 30937555540, 75736343956, 185405513889, 453879917561

Offset

0,3

Links

Alois P. Heinz, Table of n, a(n) for n = 0..1000

Wikipedia, Partition of a set

Index entries for linear recurrences with constant coefficients, signature (1,2,1,5,5,0,-3,-1).

Formula

G.f.: -(x-1)*(x+1)/(x^8+3*x^7-5*x^5-5*x^4-x^3-2*x^2-x+1).

Crossrefs

Column k=4 of A276719.

Cf. A276838, A276894.

Sequence in context: A118387 A245961 A034522 * A148339 A148340 A148341

Adjacent sequences: A276717 A276718 A276719 * A276721 A276722 A276723

Keyword

nonn,easy

Author

Alois P. Heinz, Sep 16 2016

Status

approved