A121684 Union of {8, 9, 18}, S, 2S and 4S, where S = odd squarefree numbers (A056911).

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 22, 23, 26, 28, 29, 30, 31, 33, 34, 35, 37, 38, 39, 41, 42, 43, 44, 46, 47, 51, 52, 53, 55, 57, 58, 59, 60, 61, 62, 65, 66, 67, 68, 69, 70, 71, 73, 74, 76, 77, 78, 79, 82, 83, 84, 85, 86, 87, 89, 91, 92, 93, 94, 95, 97

Offset

1,2

Comments

Numbers n such that the cyclic group Z_n is a CI-group.

The asymptotic density of this sequence is 7/Pi^2. - Amiram Eldar, May 10 2022

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

B. Alspach and M. Mishna, Enumeration of Cayley graphs and digraphs, Discr. Math., 256 (2002), 527-539.

M. Mishna, Home Page

M. Muzychuk, On Adam's conjecture for circulant graphs, Discr. Math. 167 (1997), 497-510.

Mathematica

With[{upto=100}, Select[Sort[Join[{8, 9, 18}, Flatten[{#, 2#, 4#}&/@ Select[ Range[1, upto, 2], SquareFreeQ]]]], #<=upto&]] (* Harvey P. Dale, Sep 03 2015 *)

Crossrefs

Cf. A056911, A078779, A121176.

Sequence in context: A253781 A037144 A337379 * A191853 A123093 A191932

Adjacent sequences: A121681 A121682 A121683 * A121685 A121686 A121687

Keyword

nonn

Author

N. J. A. Sloane, Sep 13 2006

Status

approved