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 A254878 #25 Mar 24 2019 06:42:09
%S A254878 4,8,32,128,168,224,756,8192,131072,524288,2147483648
%N A254878 Let 's' denote the sum of the deficient numbers in the aliquot parts of x. Sequence lists numbers x such that sigma(s) is equal to x.
%C A254878 All numbers of the form 2^A000043(n) belong to the sequence.
%C A254878 Terms that are not of this form begin: 168, 224, 756, ... - _Amiram Eldar_, Mar 24 2019
%e A254878 Aliquot parts of 8 are 1, 2, 4 that are all deficient numbers: sigma(1 + 2 + 4) = sigma(7) = 8.
%e A254878 Aliquot parts of 168 are 1, 2, 3, 4, 6, 7, 8, 12, 14, 21, 24, 28, 42, 56, 84 and the deficient numbers are 1, 2, 3, 4, 7, 8, 14, 21: sigma(1 + 2 + 3 + 4 + 7 + 8 + 14 + 21) = sigma(60) = 168.
%p A254878 with(numtheory); P:=proc(q) local a,b,c,k,n;
%p A254878 for n from 1 to q do a:=sort([op(divisors(n))]); b:=0; c:=0;
%p A254878 for k from 1 to nops(a)-1 do if sigma(a[k])<2*a[k] then b:=b+a[k]; fi; od;
%p A254878 if sigma(b)=n then print(n); fi; od; end: P(10^9);
%t A254878 seqQ[n_] := Module[{s = DivisorSum[n, # &, #<n && DivisorSigma[1,#] < 2# &]}, s>0 && DivisorSigma[1,s] == n]; Select[Range[10000], seqQ] (* _Amiram Eldar_, Mar 24 2019 *)
%o A254878 (PARI) isok(n) = my (s = sumdiv(n, d, d*((d!=n) && (sigma(d)/d < 2)))); s && (sigma(s) == n); \\ _Michel Marcus_, Feb 19 2015
%Y A254878 Cf. A000043, A000203, A005100, A254879, A254880.
%K A254878 nonn,more
%O A254878 1,1
%A A254878 _Paolo P. Lava_, Feb 10 2015
%E A254878 a(11) from _Amiram Eldar_, Mar 24 2019