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A122254 Numbers with 3-smooth Euler's totient (A000010). 6

%I

%S 1,2,3,4,5,6,7,8,9,10,12,13,14,15,16,17,18,19,20,21,24,26,27,28,30,32,

%T 34,35,36,37,38,39,40,42,45,48,51,52,54,56,57,60,63,64,65,68,70,72,73,

%U 74,76,78,80,81,84,85,90,91,95,96,97,102,104,105,108,109,111,112,114

%N Numbers with 3-smooth Euler's totient (A000010).

%C a(n) = A048135(n-2) for n>2; a(n) = A122260(n) = A048737(n) for n < 22.

%H Charles R Greathouse IV, <a href="/A122254/b122254.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[Range@115, Max[FactorInteger[EulerPhi[#]][[All, 1]]] < 5 &] (* _Ivan Neretin_, Jul 28 2015 *)

%o (PARI) is(n)=n=eulerphi(n);n>>=valuation(n,2);n==3^valuation(n,3) \\ _Charles R Greathouse IV_, Feb 21 2013

%o (PARI) list(lim)=my(v=List(),u,t);for(i=0,log(lim--+1.5)\log(3),t=3^i;while(t<=lim,if(isprime(t+1),listput(v,t+1));t<<=1));v=vecsort(Vec(v));u=List([1]);for(i=3,#v,for(j=1,#u,t=v[i]*u[j];if(t>lim,next(2));listput(u,t)));u=vecsort(Vec(u));v=List(u);for(i=1,#u,t=u[i];while((t*=3)<=lim,listput(v,t)));u=Vec(v);v=List(u);for(i=1,#u,t=u[i];while((t<<=1)<=lim,listput(v,t)));vecsort(Vec(v)) \\ _Charles R Greathouse IV_, Feb 22 2013

%Y Cf. A003586 (3-smooth).

%Y Subsequence of A122260.

%K nonn,easy

%O 1,2

%A _Reinhard Zumkeller_, Aug 29 2006

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Last modified July 21 05:11 EDT 2019. Contains 325189 sequences. (Running on oeis4.)