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A293995
Number of linear chord diagrams having n chords and no chord length larger than three.
2
1, 1, 3, 15, 35, 103, 343, 979, 2915, 8935, 26559, 79499, 239547, 717455, 2151095, 6459027, 19371507, 58106071, 174349295, 523022555, 1569013931, 4707208351, 14121515303, 42364215075, 127093528675, 381280144743, 1143838446943, 3431519977579, 10294558387995
OFFSET
0,3
FORMULA
G.f.: -(x-1)/((3*x-1)*(2*x^3-2*x^2-x-1)).
MATHEMATICA
LinearRecurrence[{2, 1, 8, -6}, {1, 1, 3, 15}, 30] (* Harvey P. Dale, Aug 08 2021 *)
CROSSREFS
Column k=3 of A293960.
Sequence in context: A338351 A145949 A015809 * A015715 A187787 A290717
KEYWORD
nonn,easy
AUTHOR
Alois P. Heinz, Oct 21 2017
STATUS
approved