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%I #13 Sep 30 2019 18:08:46
%S 0,2,3,5,6,8,9,11,14,15,17,18,20,21,23,26,27,29,30,32,33,35,36,38,39,
%T 41,42,44,45,47,48,50,51,53,54,56,57,59,63,65,66,68,69,71,72,74,75,77,
%U 78,80,81,83,86,89,90,92,93,95,96,98,99,101,102,104,105,107,108,110
%N a(n) = (A063880(n) - 108)/216.
%C Conjecture: n is a member iff 6*n+3 is squarefree. - _Vladeta Jovovic_, Aug 27 2004
%C It is only a conjecture that all terms are integers (confirmed up to 10^6 by _Robert G. Wilson v_).
%H Amiram Eldar, <a href="/A097702/b097702.txt">Table of n, a(n) for n = 1..10000</a>
%t usigma[n_] := Block[{d = Divisors[n]}, Plus @@ Select[d, GCD[ #, n/# ] == 1 &]]; (Select[ Range[ 24500], DivisorSigma[1, # ] == 2usigma[ # ] &] - 108)/216 (* _Robert G. Wilson v_, Aug 28 2004 *)
%o (PARI) {u(n)=sumdiv(n,d,if(gcd(d,n/d)==1,d))} n=2:while(1,n++: if(sigma(n)==2*u(n),print1((n-108)/216",")))
%Y Cf. A097703.
%K nonn
%O 1,2
%A _Ralf Stephan_, Aug 26 2004
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