A067135 - OEIS

%I #28 Feb 23 2024 07:25:44

%S 5,13,313,1153,26206,100318,111928,160873,363283,644278,1676428,

%T 2097808,2639518,3875998,5349238,5738773,5903638,6045583,11272903,

%U 13192933,17242333,18234403,19667998,29520643,29595193,31944238,36918448,37049803,37201813,43522288

%N Numbers k such that sigma(k+2) = 2*sigma(k-2).

%C For each term given here except 5, k+2 is divisible by 3, but that's not always true: k=149784995358 is a counterexample. Also, k+2 is divisible by 5 for all terms here except 5 and 26206, but it is also not true for k=70333261.

%H Vincenzo Librandi and Donovan Johnson, <a href="/A067135/b067135.txt">Table of n, a(n) for n = 1..500</a> (first 80 terms from Vincenzo Librandi)

%t Do[If[DivisorSigma[1, n+2] == 2*DivisorSigma[1, n-2], Print[n]], {n, 2, 10^9}] (* _Ryan Propper_, Sep 26 2005 *)

%Y Cf. A067134.

%K nonn

%O 1,1

%A _Benoit Cloitre_, Feb 18 2002

%E Edited by _Dean Hickerson_, Feb 20 2002

%E More terms from _Ryan Propper_, Sep 26 2005