Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #14 Jul 13 2019 03:43:25
%S 8,12,16,20,24,25,27,28,32,36,40,44,45,48,50,52,54,56,60,63,64,68,72,
%T 75,76,80,81,84,88,90,92,96,99,100,104,108,112,116,117,120,124,125,
%U 126,128,132,135,136,140,144,147,148,150,152,153,156,160,162,164,168,169
%N Nonsquarefree numbers whose Euler totient function is also nonsquarefree.
%C Prime powers with sufficiently large exponents are in this sequence, including 8, 16, 32, 64, ..., 27, 81, ..., 25, 125.
%H Amiram Eldar, <a href="/A049199/b049199.txt">Table of n, a(n) for n = 1..10000</a>
%F k such that abs(mu(k)) = 0 and abs(mu(phi(k))) = 0.
%e 124 = 4*31 is in the sequence because phi(124)=60 and neither 124 nor 60 is squarefree.
%t Select[Range[170], !SquareFreeQ[#] && !SquareFreeQ[EulerPhi[#]] &] (* _Amiram Eldar_, Jul 13 2019 *)
%o (PARI) isok(n) = !issquarefree(n) && ! issquarefree(eulerphi(n)); \\ _Michel Marcus_, Jul 13 2019
%Y Cf. A000010, A005117, A013929, A049198.
%K nonn
%O 1,1
%A _Labos Elemer_