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 A103877 #4 Jan 04 2013 14:44:58
%S A103877 1,3,4,6,7,9,10,12,13,15,18,21,16,24,19,27,22,30,25,33,28,31,34,36,37,
%T A103877 39,40,42,43,45,48,51,54,57,46,60,49,63,52,66,55,58,61,64
%N A103877 Position of n in rearrangement of natural numbers A103849.
%C A103877 a(43)=64 because 43 in 64th place in A103849.
%t A103877 Flatten[Table[Position[A103849, i], {i, 0, 43}]]
%Y A103877 Cf. A036301, A103829, A103848, A103849.
%K A103877 nonn,base
%O A103877 0,2
%A A103877 _Zak Seidov_, Feb 20 2005