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 A075333 #10 Mar 08 2015 18:05:13 %S A075333 2,4,8,10,13,16,19,21,23,28,30,33,36,38,42,43,48,52,54,55,60,63,65,69, %T A075333 71,75,77,80,82,84,87,92,94,96,98,102,104,107,111,113,116,119,121,124, %U A075333 126,128,134,137,140,142,144,148,150,153,154,159,162,166,168,172,174 %N A075333 Pair up the natural numbers as (r, s) (say) so that all natural numbers are obtained only once as r, s, s+r, s-r or r*s: (2, 3), (4, 11), (8, 17), (10, 22), (13, 27), (16, 34), ... Sequence gives first member of each pair. %C A075333 The first pair starts with 2 and not with 1 as in (1,k) k occurs as 1*k (of the form r*s) and k (of the form s) itself, i.e., in two ways. %H A075333 Joshua Zucker, Feb 24 2008, <a href="/A075333/b075333.txt">Table of n, a(n) for n = 1..151</a> %Y A075333 Cf. A075334, A075335, A075336, A075337. %K A075333 nonn %O A075333 1,1 %A A075333 _Amarnath Murthy_, Sep 18 2002 %E A075333 Corrected and extended by _Joshua Zucker_, Feb 24 2008