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

Author

N. J. A. Sloane, Sep 13 2006

Keywords

• nonn

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.

Crossrefs

Cf. A056911, A078779, A121176.

Programs

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 *)