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%I #16 Mar 28 2013 16:18:36
%S 1,2,7,19,358,3845,31138,36461,4286729,81945545,2059172170,3071920146,
%T 9331669953,19026491086
%N Numbers n such that sigma(n) divides sum_{k=1..n} tau(k), where tau(k) is the number of divisors of k (A000005) and sigma(n) is the sum of divisors of n (A000203).
%C a(15) > 5*10^10. - _Donovan Johnson_, Apr 16 2012
%t Select[Range[1000000], Mod[Sum[DivisorSigma[0, n], {n, #}], DivisorSigma[1, #]] == 0 &] (* _Jayanta Basu_, Mar 28 2013 *)
%o (PARI) s=0;for(n=1,1e6,if((s+=numdiv(n))%sigma(n)==0,print1(n", "))) \\ _Charles R Greathouse IV_, Apr 16 2012
%Y Cf. A006218.
%K nonn
%O 1,2
%A _Naohiro Nomoto_, Apr 16 2012
%E a(10) from _Charles R Greathouse IV_, Apr 16 2012
%E a(11)-a(14) from _Donovan Johnson_, Apr 16 2012