A153162 - OEIS

%I #6 Mar 30 2012 18:51:00

%S 2,5,5,8,7,7,8,11,13,12,9,9,12,13,11,14,19,21,18,17,19,16,11,11,16,19,

%T 17,18,21,19,14,17,25,30,27,29,34,31,23,22,29,31,26,23,25,20,13,13,20,

%U 25,23,26,31,29,22,23,31,34,29,27,30,25,17,20,31,39,36,41,49,46,35,37

%N Denominators of Stern-Brocot tree hanging between 1/3 and 2/3; numerators=A153161.

%C For all coprime pairs (u,v) with 1/3 < u/v < 2/3 exists a unique k such that A153161(k)=u and a(k)=v;

%C a(1) = 2 and for n>1: a(n) = if A025480(n-1)<>0 and A025480(n)<>0 then a(A025480(n-1))+a(A025480(n)) else if A025480(n)=0 then a(A025480(n-1))+3 else a(n)=3+a(A025480(n-1)).

%H <a href="/index/St#Stern">Index entries for sequences related to Stern's sequences</a>

%H N. J. A. Sloane, <a href="/stern_brocot.html">Stern-Brocot or Farey Tree</a>

%Y A047679, A007306.

%K frac,nonn,tabf

%O 1,1

%A _Reinhard Zumkeller_, Dec 22 2008