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%I #14 Jun 24 2014 01:08:20
%S 119,1559,2939,17759,19919,32219,33839,55964,71039,186779,308039,
%T 511499,523775,553499,699359,838214,1048904,1159379,1328939,1333247,
%U 1700039,2462687,2703887,2956079,3115319,3561095,3764207,3972695,7625879,7852919,8048963
%N Numbers n such that sigma(n+1) = 2*sigma(n-1).
%C For each term given here, n+1 is divisible by 3, but that's not always true; n=12396999 is a counterexample.
%H Donovan Johnson, <a href="/A067134/b067134.txt">Table of n, a(n) for n = 1..1000</a>
%t Flatten[Position[Partition[DivisorSigma[1,Range[8100000]],3,1],_?(Last[#] == 2*First[#]&),{1},Heads->False]]+1 (* _Harvey P. Dale_, Aug 19 2013 *)
%o (PARI) s1=1; s2=3; for(n=2, 10^8, s3=sigma(n+1); if(s3==2*s1, print1(n ", ")); s1=s2; s2=s3) /* _Donovan Johnson_, Apr 06 2013 */
%Y Cf. A055574, A067135.
%K nonn
%O 1,1
%A _Benoit Cloitre_, Feb 18 2002
%E Edited by _Dean Hickerson_, Feb 20 2002