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 A119272 #6 May 12 2015 12:44:57 %S A119272 0,0,1,2,2,3,6,6,3,4,10,15,12,12,15,10,4,5,14,24,21,28,40,35,20,20,35, %T A119272 40,28,21,24,14,5,6,18,33,30,44,65,60,36,45,84,104,77,70,88,63,30,30, %U A119272 63,88,70,77,104,84,45,36,60,65,44,30,33,18,6,7,22,42,39,60,90,85,52,70 %N A119272 Product of numerator and denominator in Stern-Brocot tree. %C A119272 The sum of the reciprocals of each row (n > 0) is 1 (i.e., 1/1, 1/2 + 1/2, 1/3 + 1/6 + 1/6 + 1/3, 1/4 + ... + 1/4, 1/5 + ... + 1/5, ...). The cut-the-knot link gives credit to Pierre Lamothe for this observation. %H A119272 Ivan Neretin, <a href="/A119272/b119272.txt">Table of n, a(n) for n = 1..4097</a> %H A119272 Alexander Bogomolny, <a href="http://www.cut-the-knot.org/blue/Stern.shtml">Cut-the-knot on Stern-Brocot trees</a> %F A119272 Take each row of A049449 and append its reverse. %F A119272 Also, a(n) = A007305(n-1)*A047679(n-3) for n>=3. %Y A119272 Cf. A049449 (has the first half of each row), A007305 (numerators), A047679 (denominators). %K A119272 nonn,tabf %O A119272 1,4 %A A119272 _Joshua Zucker_, May 11 2006