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A261480 Number of set partitions of [n] into exactly four parts such that no part contains two elements with a circular distance less than three. 2
1, 0, 3, 7, 7, 21, 50, 77, 164, 364, 672, 1330, 2787, 5474, 10797, 21945, 43841, 87031, 174812, 350175, 698302, 1397550, 2798250, 5591460, 11181661, 22374660, 44740503, 89467147, 178965787, 357927801, 715796390, 1431659537, 2863370744, 5726556304, 11453194452 (list; graph; refs; listen; history; text; internal format)
OFFSET

4,3

LINKS

Alois P. Heinz, Table of n, a(n) for n = 4..1000

Index entries for linear recurrences with constant coefficients, signature (0,1,5,4,-1,-4,-4).

FORMULA

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

EXAMPLE

a(4) = 1: 1|2|3|4.

a(6) = 3: 14|25|3|6, 14|2|36|5, 1|25|36|4.

a(7) = 7: 14|25|36|7, 14|25|37|6, 14|26|37|5, 15|26|37|4, 15|26|3|47, 15|2|36|47, 1|25|36|47.

a(8) = 7: 14|26|37|58, 14|27|36|58, 15|26|37|48, 15|26|38|47, 15|27|36|48, 16|25|37|48, 16|25|38|47.

CROSSREFS

Column k=4 of A261477.

Sequence in context: A157102 A226512 A270307 * A121172 A322934 A077629

Adjacent sequences:  A261477 A261478 A261479 * A261481 A261482 A261483

KEYWORD

nonn,easy

AUTHOR

Alois P. Heinz, Aug 20 2015

STATUS

approved

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Last modified September 18 07:50 EDT 2019. Contains 327168 sequences. (Running on oeis4.)