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 A153800 #8 Dec 15 2016 15:23:53 %S A153800 2,3,5,7,13,19,25,41,110,192,229,294 %N A153800 Indices of perfect numbers (A000396) in the sequence of multiply-perfect numbers (A007691). %C A153800 The sequence contains no further entries between 294 and 1600. - _R. J. Mathar_, May 26 2011 %e A153800 a(7) is 25 because the 25th multiply-perfect number A007691(25)=137438691328 is also the 7th perfect number A000396(7). %Y A153800 Cf. A000396, A007691. %K A153800 more,nonn %O A153800 1,1 %A A153800 _Omar E. Pol_, Jan 13 2009