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%I #10 Nov 21 2013 12:48:13
%S -2,-5,-2,3,2,-19,19,-41,-7,-41,17,2,-109,-2,7,-47,-271,199,-127,71,2,
%T -37,499,2,-71,199,353,-811,1021,-929,59,-457,-449,-163,-683,-157,41,
%U -751,251,2,-2161,-19,401,467,-61,967,-631,-3659,-2777,3391,-4421,269,-2333,-1201,-4969,4999,-1103,-2647,-1097,269
%N Abundance values which are +1 or -1 times a prime.
%F Solutions x to sigma[n]-2n=x where Abs[x] is a prime number.
%e n=18: sigma[18]=18+9+6+3+2+1=39, 2n=36, abundance=3, a prime;
%e n=25: sigma[25]=25+5+1=31, 2n=50, abundance=-19.
%t ab[x_] := DivisorSigma[1, x]-2*x Do[If[PrimeQ[s=ab[n]], Print[s]], {n, 1, 10000}]
%t Select[Table[DivisorSigma[1,n]-2n,{n,7000}],PrimeQ[Abs[#]]&] (* _Harvey P. Dale_, Aug 21 2011 *)
%Y Cf. A000203, A000040, A077374, A087998, A088005.
%K sign
%O 1,1
%A _Labos Elemer_, Oct 18 2003
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