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A287582
Number of set partitions of [n] such that all absolute differences between least elements of consecutive blocks and between consecutive elements within the blocks are not larger than three.
2
1, 1, 2, 5, 15, 46, 139, 410, 1189, 3397, 9615, 27056, 75838, 212088, 592314, 1652806, 4609789, 12853354, 35832568, 99884249, 278414160, 776016655, 2162929636, 6028494326, 16802444328, 46831107603, 130525521011, 363794294041, 1013948759937, 2826024652739
OFFSET
0,3
LINKS
FORMULA
G.f.: -(2*x^9+7*x^8-6*x^6-x^5+11*x^4+x^3-3*x+1) / ((x^2+x-1) * (2*x^6 +3*x^5 -6*x^3 -3*x^2 -x+1) * (x-1)^2).
a(n) = A000110(n) for n <= 4.
CROSSREFS
Column k=3 of A287417.
Cf. A000110.
Sequence in context: A149913 A065848 A148359 * A122392 A139782 A378339
KEYWORD
nonn,easy
AUTHOR
Alois P. Heinz, May 26 2017
STATUS
approved