A068919 Squarefree orders of non-Abelian groups.

6, 10, 14, 21, 22, 26, 30, 34, 38, 39, 42, 46, 55, 57, 58, 62, 66, 70, 74, 78, 82, 86, 93, 94, 102, 105, 106, 110, 111, 114, 118, 122, 129, 130, 134, 138, 142, 146, 154, 155, 158, 165, 166, 170, 174, 178, 182, 183, 186, 190, 194, 195, 201, 202, 203, 205, 206

Offset: 1

Author

Sharon Sela (sharonsela(AT)hotmail.com), Mar 29 2002

Keywords

• nonn

Comments

This set is the difference A005117 \ A003277, that is, the squarefree numbers that are not cyclic (A003277). - Jeppe Stig Nielsen, Sep 25 2017

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Intersection of A060652 and A005117.

Cf. A064899.

Also intersection of A056868 and A005117. - Reinhard Zumkeller, Jun 28 2013

Cf. A008966.

Programs

Haskell

a068919 n = a068919_list !! (n-1)
a068919_list = filter ((== 1) . a008966) a056868_list
-- Reinhard Zumkeller, Jun 28 2013

Mathematica

Complement[Select[Range[206], SquareFreeQ[#] &],
Select[Range[206], FiniteGroupCount[#] == 1 &]] (* Geoffrey Critzer, Nov 28 2015 *)

PARI

is(n)=issquarefree(n)&&gcd(n,eulerphi(n))!=1 \\ Jeppe Stig Nielsen, Sep 25 2017