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 A280817 #11 Jan 10 2017 07:52:54
%S A280817 0,0,1,0,2,2,1,0,2,5,2,3,3,2,2,0,5,1,4,9,1,5,2,4,0,9,4,3,4,5,1,0,2,7,
%T A280817 2,5,6,4,3,11,9,2,5,9,7,5,2,5,3,6,5,8,7,4,5,4,4,11,4,9,5,2,6,0,9,5,6,
%U A280817 6,2,5,5,2,11,9,5,7,2,9,4,13,4,6,9,3,7,7,4,11,11,15,3,9,1,5,4,6,8,9,7,7,8,7,6,13,2,11,7,7,8
%N A280817 a(n) = A049501(sigma(n)).
%C A280817 a(n) = major index (1st definition) of the sum of the divisors of n, i.e., sigma(n).
%H A280817 Indranil Ghosh, <a href="/A280817/b280817.txt">Table of n, a(n) for n = 1..10000</a>
%H A280817 Indranil Ghosh, <a href="/A280817/a280817.txt">Python Program to generate the sequence</a>
%F A280817 a(n) = A049501(A000203(n)).
%e A280817 For n = 10, sigma(n) = 18 and major index (1st definition) of 18 is 5. So, a(10) = 5.
%t A280817 Table[Total@ Flatten@ Position[Partition[IntegerDigits[DivisorSigma[1, n], 2], 2, 1], {1, 0}], {n, 120}] (* _Michael De Vlieger_, Jan 10 2017, after _Harvey P. Dale_ at A049501 *)
%Y A280817 Cf. A049501, A000203, A280726, A280800.
%K A280817 nonn
%O A280817 1,5
%A A280817 _Indranil Ghosh_, Jan 08 2017