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%I #18 Aug 15 2021 21:50:52
%S 1,2,11,19,36,45,152,377,418,3794,4423,14495,31148,42224,49279,120447,
%T 1018376,2605261,17484247,368070997,850833878,1121254607,3440701629,
%U 7863041200
%N Numbers k that divide the alternating sum sigma(1) - sigma(2) + sigma(3) - sigma(4) + ... + ((-1)^(k+1))*sigma(k).
%C No further term below 10^7.
%C a(25) > 5*10^10. - _Donovan Johnson_, Jul 26 2011
%e sigma(1) - sigma(2) = -2, which is divisible by 2, so 2 is a term of the sequence.
%t s = 0; Do[s = s + (-1)^(i + 1) * DivisorSigma[1, i]; If[Mod[s, i] == 0, Print[i]], {i, 1, 10^5}]
%o (PARI) {a067931(m)=local(s,n); s=0; for(n=1,m, if(n%2==0,s=s-sigma(n),s=s+sigma(n)); if(s%n==0,print1(n,",")))}
%Y Cf. A000203, A068762.
%K nonn,more
%O 1,2
%A _Joseph L. Pe_, Feb 22 2002
%E Edited and extended by _Klaus Brockhaus_, Feb 28 2002
%E a(19)-a(24) from _Donovan Johnson_, Jul 26 2011
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