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A334625
Maximal size of a subset T of S = {1,2,...,n} with a cyclic arrangement of T such that any three neighbors can be reordered in an arithmetic progression.
2
3, 3, 3, 3, 3, 3, 9, 9, 9, 9, 12, 12, 15, 15, 15, 15, 18, 18, 21, 21, 21, 21, 24, 24, 27, 27, 27, 27, 30, 30, 33, 33, 33, 33, 36, 36, 39, 39, 39, 39, 42, 42, 45, 45, 45, 45, 48, 48, 51, 51, 51, 51, 54, 54, 57, 57, 57, 57, 60, 60
OFFSET
3,1
LINKS
FORMULA
Conjectures from Colin Barker, Sep 10 2020: (Start)
G.f.: 3*x^3*(1 + x^6 + x^10 - x^12) / ((1 - x)^2*(1 + x)*(1 - x + x^2)*(1 + x + x^2)).
a(n) = a(n-1) + a(n-6) - a(n-7) for n>15.
(End)
CROSSREFS
Cf. A336351.
Sequence in context: A351836 A105159 A365458 * A209291 A375642 A332875
KEYWORD
nonn
AUTHOR
STATUS
approved