A266969 Integers n such that A001006(n) is divisible by n.

1, 2, 21, 266, 387, 657, 1314, 6291, 16113, 25767, 27594, 41902, 54243, 55314, 56457, 89018, 96141

Offset

1,2

Comments

Integers n such that number of ways of drawing any number of nonintersecting chords joining n (labeled) points on a circle is divisible by n.

Corresponding values of A001006(n)/n are 1, 1, 6787979, ...

Links

Table of n, a(n) for n=1..17.

Example

There are 142547559 ways to join 21 points on a circle by nonintersecting chords. Because of the fact that 142547559 is divisible by 21, 21 is a term of this sequence.

Mathematica

lim = 100000; t = CoefficientList[Series[(1 - x - (1 - 2 x - 3 x^2)^(1/2))/(2 x^2), {x, 0, lim}], x]; Select[Range@ lim, Divisible[t[[# + 1]], #] &] (* Michael De Vlieger, Jan 09 2016, after Jean-François Alcover at A001006 *)

Crossrefs

Cf. A001006, A081735.

Sequence in context: A045726 A105712 A087677 * A229036 A097627 A094797

Adjacent sequences: A266966 A266967 A266968 * A266970 A266971 A266972

Keyword

nonn,more

Author

Altug Alkan, Jan 07 2016

Extensions

a(8)-a(17) from Michael De Vlieger, Jan 09 2016

Status

approved