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A122254 Numbers with 3-smooth Euler's totient (A000010). 6
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, 34, 35, 36, 37, 38, 39, 40, 42, 45, 48, 51, 52, 54, 56, 57, 60, 63, 64, 65, 68, 70, 72, 73, 74, 76, 78, 80, 81, 84, 85, 90, 91, 95, 96, 97, 102, 104, 105, 108, 109, 111, 112, 114 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

MATHEMATICA

Select[Range@115, Max[FactorInteger[EulerPhi[#]][[All, 1]]] < 5 &] (* Ivan Neretin, Jul 28 2015 *)

PROG

(PARI) is(n)=n=eulerphi(n); n>>=valuation(n, 2); n==3^valuation(n, 3) \\ Charles R Greathouse IV, Feb 21 2013

(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

CROSSREFS

Cf. A003586 (3-smooth).

Subsequence of A122260.

Sequence in context: A023752 A048737 A122260 * A249626 A102823 A179308

Adjacent sequences:  A122251 A122252 A122253 * A122255 A122256 A122257

KEYWORD

nonn,easy

AUTHOR

Reinhard Zumkeller, Aug 29 2006

STATUS

approved

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Last modified October 20 10:41 EDT 2019. Contains 328257 sequences. (Running on oeis4.)