A068919 - OEIS

%I #15 Sep 25 2017 12:56:05

%S 6,10,14,21,22,26,30,34,38,39,42,46,55,57,58,62,66,70,74,78,82,86,93,

%T 94,102,105,106,110,111,114,118,122,129,130,134,138,142,146,154,155,

%U 158,165,166,170,174,178,182,183,186,190,194,195,201,202,203,205,206

%N Squarefree orders of non-Abelian groups.

%C This set is the difference A005117 \ A003277, that is, the squarefree numbers that are not cyclic (A003277). - _Jeppe Stig Nielsen_, Sep 25 2017

%H Reinhard Zumkeller, <a href="/A068919/b068919.txt">Table of n, a(n) for n = 1..10000</a>

%t Complement[Select[Range[206], SquareFreeQ[#] &],

%t Select[Range[206], FiniteGroupCount[#] == 1 &]] (* _Geoffrey Critzer_, Nov 28 2015 *)

%o (Haskell)

%o a068919 n = a068919_list !! (n-1)

%o a068919_list = filter ((== 1) . a008966) a056868_list

%o -- _Reinhard Zumkeller_, Jun 28 2013

%o (PARI) is(n)=issquarefree(n)&&gcd(n,eulerphi(n))!=1 \\ _Jeppe Stig Nielsen_, Sep 25 2017

%Y Intersection of A060652 and A005117.

%Y Cf. A064899.

%Y Also intersection of A056868 and A005117. - _Reinhard Zumkeller_, Jun 28 2013

%Y Cf. A008966.

%K nonn

%O 1,1

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