A144857 Numbers k that divide Sum_{i=1..k} phi(i)^2, where phi(i) = totient function A000010.
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
Offset: 1
Programs
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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 *) -
PARI
s=0;for(n=1,1e6,s+=eulerphi(n)^2;if(s%n==0,print1(n", "))) \\ Charles R Greathouse IV, Mar 05 2013
Formula
{k: k | A057434(k)}. - R. J. Mathar, Sep 29 2008
Extensions
a(8)-a(11) 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
Comments