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 A153803 #7 Dec 24 2016 11:34:36
%S A153803 0,0,0,0,0,2,6,10,49,103,122,167
%N A153803 a(n) = A153800(n) - A000043(n).
%t A153803 a007691[m_] := Block[{f = 0, i = 1}, While[f < m, If[Divisible[DivisorSigma[1, i], i], ++f]; ++i;]; Return[i - 1]]
%t A153803 a153800[n_] := Block[{i = 2, j, f = 0}, While[f < n, j = a007691[i]; If[PerfectNumberQ[j], ++f;]; ++i]; Return[i - 1]]
%t A153803 a[n_] := a153800[n] - MersennePrimeExponent[n]
%t A153803 a /@ Range[1, 4] (* _Julien Kluge_, Dec 15 2016 *)
%Y A153803 Cf. A000040, A000043, A000668, A000225, A000396, A007691, A153800, A153801, A153802.
%K A153803 more,nonn
%O A153803 1,6
%A A153803 _Omar E. Pol_, Jan 13 2009