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 A138873 #18 Sep 26 2020 14:00:10
%S A138873 6,28,49,81,33,85,13,23,26,19,13,14,23,14,54,10,99,33,18,40,11,59,39,
%T A138873 93,10,81,36,14,13,13,27,15,83,84,33,19,81,95,42,79,44,74,49,77,20,14,
%U A138873 50
%N A138873 First two digits of n-th even perfect number.
%H A138873 Jan Munch Pedersen, <a href="http://amicable.homepage.dk/perfect.htm">Known Perfect Numbers</a> [Steven Bi (chenhsi(AT)stanford.edu), Jan 18 2009]
%H A138873 Omar E. Pol, <a href="http://www.polprimos.com/#Los%20n%C3%BAmeros%20perfectos">Los numeros perfectos</a>
%t A138873 Join[{6},FromDigits[Take[IntegerDigits[#],2]]&/@PerfectNumber[Range[2,50]]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Sep 26 2020 *)
%Y A138873 Cf. A000396, A138862, A138875.
%Y A138873 First 2 digits of sequence A138875. [Steven Bi (chenhsi(AT)stanford.edu), Jan 18 2009]
%K A138873 base,more,nonn
%O A138873 1,1
%A A138873 _Omar E. Pol_, Apr 02 2008
%E A138873 a(15)-a(31) added by Steven Bi (chenhsi(AT)stanford.edu), Jan 18 2009
%E A138873 Definition changed (inserting the word "even") and a(37)-a(47) added by _Ivan Panchenko_, Aug 04 2018