This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A286844 #20 Jun 17 2025 00:38:06
%S A286844 1,2,3,4,2,4,2,3,6,1,2,4,3,4,5,7,6,5,6,7,6,7,4,2,4,3,8,5,6,8,6,2,8,3,
%T A286844 7,4,8,6,10,10,7,10,9,10,12,10,2,4,6,11,7,4,10,6,5,7,11,2,3,9,5,8,6,8,
%U A286844 12,7,11,10,12,1,3,11,4,10,8,7,10,4,15,12,6
%N A286844 a(n) = log_2(A286843(n) - A001065(A286843(n))).
%e A286844 A286843(1) - A001065(A286843(1)) = 10 - 8 = 2 = 2^1, thus a(1) = 1.
%t A286844 t=Select[Table[2n,{n,1,7*10^7}],DivisorSigma[1, 2#-DivisorSigma[1,#]]+1 == 2(2#-DivisorSigma[1,#])>2 &]; u=Table[2t[[k]]-DivisorSigma[1,t[[k]]],{k,81}]; Log[2,u] (* or *)
%t A286844 Select[Log2[2 # - DivisorSigma[1, #]] & /@ (2 Range@33500), IntegerQ[#] && # > 0 &] (* _Giovanni Resta_, Aug 08 2017 *)
%Y A286844 Cf. A000079, A001065, A286843.
%K A286844 nonn
%O A286844 1,2
%A A286844 _XU Pingya_, Aug 07 2017