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 A140109 #4 Mar 30 2012 18:52:25 %S A140109 7,15,20,42,7,24,25,84,13,14,15,84,13,84,85,546,17,8,15,60,17,9,10,36, %T A140109 29,20,21,210,37,12,35,210,41,9,40,180,53,45,48,1080,73,48,55,1320,89, %U A140109 39,80,1560,97,65,72,2340,101,20,99,990,109,60,91,2730,113,15,112,840 %N A140109 Quartets of prime x, composites y, z and S for Heron's formula. %C A140109 Heron's formula (x+y+z)*(x+y-z)*(x+z-y)*(y+z-x)/16=S^2 %e A140109 The quartets are: (7, 15, 20, 42), (7, 24, 25, 84), (13, 14, 15, 84), etc. %Y A140109 Cf. A140385, A140391, A140384. %K A140109 nonn %O A140109 1,1 %A A140109 _Juri-Stepan Gerasimov_, Jul 10 2008 %E A140109 This should be replaced by four linked sequences! As it stands it is not a proper sequence. - _N. J. A. Sloane_, Jul 11 2008