A015881 - OEIS

%I #28 Feb 10 2024 11:36:03

%S 28,154,466,874,958,1054,2266,2878,11505,12754,14674,17974,21154,

%T 21778,29223,29535,31725,32714,39658,43186,48004,52018,62338,70198,

%U 126795,132783,163251,164818,207603,212938,221595,272685,274527

%N Numbers k such that sigma(k) = sigma(k+11).

%H Donovan Johnson, <a href="/A015881/b015881.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[300000], DivisorSigma[1, #]==DivisorSigma[1, # + 11] &] (* _Vincenzo Librandi_, Mar 10 2014 *)

%t Position[Partition[DivisorSigma[1,Range[300000]],12,1],_?(First[#]== Last[#]&), 1,Heads->False]//Flatten (* _Harvey P. Dale_, Aug 20 2017 *)

%o (PARI) is(n)=sigma(n)==sigma(n+11) \\ _Charles R Greathouse IV_, Mar 09 2014

%Y Cf. A002961, A007373, A015861, A015863, A015865, A015866, A015867, A015876, A015877, A015880, A015882, A015883, A181647.

%K nonn

%O 1,1

%A _Robert G. Wilson v_