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%I
%S 513,703,999,1026,1387,1406,1539,1971,1998,2071,2413,2774,2943,2997,
%T 3078,3097,3429,3439,3781,3942,4142,4401,4617,4699,4826,4887,5149,
%U 5373,5833,5886,5913,5994,6031,6194,6858,6878,7201,7317,7363,7543,7562
%N Numbers k such that Euler phi(k) / Carmichael lambda(k) = 18.
%t Select[Range[8000],EulerPhi[#]/CarmichaelLambda[#]==18&] (* _Harvey P. Dale_, Jun 06 2018 *)
%o (PARI) {cmf(f)=if( ((f[1]==2)&&(f[2]>2)),eulerphi(f[1]^f[2])/2, eulerphi(f[1]^f[2])) } {cl(f)= k=factor(f); l=1; for(x=1,omega(f),l=lcm(l,cmf([k[x,1], k[x,2]]))); l } {A0(n)=eulerphi(n)/cl(n)} for(x=1,10001, if(A0(x)==18,print1(x,",")))
%o (PARI) isok(k) = eulerphi(k)/lcm(znstar(k)[2]) == 18; \\ _Michel Marcus_, May 25 2022
%Y Cf. A000010, A002322.
%K easy,nonn,changed
%O 1,1
%A _Randall L Rathbun_, Jan 12 2002
%E Corrected by _T. D. Noe_, Nov 01 2006
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