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A144857 Numbers n such that n divides Sum_{i=1..n} phi(i)^2, where phi(i) = totient function A000010. 1
1, 2, 3, 6, 26, 190, 610, 2078, 2670, 7038, 16466, 89973, 150374, 157298, 163367, 419090, 640627, 879702, 3479689, 5618437, 11304721, 74106171, 471591726, 475915439, 1198344149, 2270643086, 3051266010 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Does an n exist such that RootMeanSquare(phi(1),...,phi(n)) is an integer ?

LINKS

Table of n, a(n) for n=1..27.

FORMULA

{n: n | A057434(n)}. - R. J. Mathar, Sep 29 2008

MATHEMATICA

lst = {}; s = 0; Do[ s = s + EulerPhi[n]^2; If[ Mod[s, n] == 0, AppendTo[lst, n]], {n, 10^9}]; lst (* Robert G. Wilson v, Oct 02 2008 *)

PROG

(PARI) s=0; for(n=1, 1e6, s+=eulerphi(n)^2; if(s%n==0, print1(n", "))) \\ Charles R Greathouse IV, Mar 05 2013

CROSSREFS

Cf. A000010, A048290, A140480.

Sequence in context: A333420 A296259 A000341 * A090445 A228346 A269996

Adjacent sequences:  A144854 A144855 A144856 * A144858 A144859 A144860

KEYWORD

nonn

AUTHOR

Ctibor O. Zizka, Sep 23 2008

EXTENSIONS

Four more terms from R. J. Mathar, Sep 29 2008

a(12)-a(24) from Robert G. Wilson v, Oct 02 2008

a(25)-a(27) from Donovan Johnson, Aug 21 2011

STATUS

approved

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Last modified January 23 12:31 EST 2021. Contains 340385 sequences. (Running on oeis4.)