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 A294886 #14 Mar 14 2024 03:48:55
%S A294886 0,1,1,3,1,6,1,7,4,8,1,10,1,10,9,15,1,15,1,22,11,14,1,18,6,16,13,28,1,
%T A294886 36,1,31,15,20,13,19,1,22,17,30,1,48,1,40,33,26,1,34,8,43,21,46,1,42,
%U A294886 17,36,23,32,1,40,1,34,41,63,19,72,1,58,27,74,1,27,1,40,49,64,19,84,1,46,40,44,1,52,23,46,33,92,1,90,21
%N A294886 Sum of deficient proper divisors of n.
%C A294886 Sum of divisors of n smaller than n that are deficient numbers (in A005100).
%H A294886 Antti Karttunen, <a href="/A294886/b294886.txt">Table of n, a(n) for n = 1..20000</a>
%H A294886 <a href="/index/Su#sums_of_divisors">Index entries for sequences related to sums of divisors</a>
%F A294886 a(n) = Sum_{d|n, d<n} A294934(d)*d.
%F A294886 a(n) = A187793(n) - (A294934(n)*n).
%F A294886 a(n) + A294887(n) = A001065(n).
%e A294886 Proper divisors of 90 are: 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45. Of these 1, 2, 3, 5, 9, 10, 15 and 45 are in A005100, thus a(90) = 1+2+3+5+9+10+15+45 = 90.
%t A294886 a[n_] := DivisorSum[n, # &, # < n && DivisorSigma[1, #] < 2*# &]; Array[a, 100] (* _Amiram Eldar_, Mar 14 2024 *)
%o A294886 (PARI) A294886(n) = sumdiv(n, d, (d<n)*(sigma(d)<(2*d))*d);
%Y A294886 Cf. A001065, A005100, A001065, A187793, A294926, A294934, A294887, A294888, A294889.
%Y A294886 Cf. A125310 (fixed points).
%K A294886 nonn
%O A294886 1,4
%A A294886 _Antti Karttunen_, Nov 14 2017