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A088006 Abundance values which are +1 or -1 times a prime. 1

%I

%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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Last modified October 22 22:34 EDT 2019. Contains 328335 sequences. (Running on oeis4.)