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%I #14 Dec 12 2016 05:20:34
%S 5491,8075,25317,27455,71383,72283,76131,104975,138575,193041,203167,
%T 295569,295947,298775,334951,356915,361415,400843,451535,492275,
%U 509575,572975,589475,595975,654493,683757,815975,862087,876627,919075,936729
%N Nonsquarefree "year numbers" (numbers n such that phi(n) = 2 phi(sigma(n)): A137815).
%C This is the subsequence of nonsquarefree elements of A137815. See there for more comments and references.
%C There are only 32 such numbers below 10^6, 145 below 10^7 and 785 below 10^8.
%H M. F. Hasler, <a href="/A137816/b137816.txt">Table of n, a(n) for n=1,...,785</a>.
%t Reap[For[n=1, n<10^6, n++, If[!SquareFreeQ[n] && EulerPhi[n] == 2*EulerPhi[ DivisorSigma[1, n]], Print[n]; Sow[n]]]][[2, 1]] (* _Jean-François Alcover_, Dec 12 2016 *)
%o (PARI) { for( n=1,10^8, !issquarefree(n) && eulerphi(n)==2*eulerphi(sigma(n)) && print1(n", "))
%Y Cf. A137815-A137819, A006872, A067704.
%K nonn
%O 1,1
%A _R. K. Guy_, _R. J. Mathar_ and _M. F. Hasler_, Feb 11 2008
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