%N Consider the Farey tree A006842/A006843; a(n) = row at which the denominator n first appears (assumes first row is labeled row 1).
%C Computed by Alan Wechsler, Dec 16, 2010.
%C Richard C. Schroeppel also asked about the analogous sequence giving the last occurrence of denominator n.
%D Based on a posting by Richard C. Schroeppel to the Math Fun Mailing List, Dec 15 2010.
%H Bo Gyu Jeong, <a href="/A178031/b178031.txt">Table of n, a(n) for n = 1..10000</a>
%H Richard J. Mathar, <a href="http://www.mpia.de/~mathar/public/mathar20171127.pdf">The Kepler binary tree of reduced fractions</a>, 2017.
%Y See A178047 for another version. Cf. A006842, A006843, A177903, A178042.
%A _N. J. A. Sloane_, Dec 16 2010
%E More terms from _Bo Gyu Jeong_, Oct 20 2012