%I A013642
%S A013642 3,6,8,11,12,15,18,20,24,27,30,35,38,39,40,42,48,51,56,63,66,68,72,80,
               83,
%T A013642 84,87,90,99,102,104,105,110,120,123,132,143,146,147,148,150,152,156,168,
%U A013642 171,182,195,198,200,203,210,224,227,228,230,231,235,240,255,258,260,264
%N A013642 Numbers n such that continued fraction for sqrt(n) has period 2.
%C A013642 This sequence is identical to the sequence of numbers of the form n = 
               a^2 + b, where a and b are positive integers and b is a factor of 
               2a greater than 1, in which case the continued fraction expansion 
               of sqrt(n) is [a; [2a/b, 2a]]. - David Terr (David_C_Terr(AT)raytheon.com), 
               Jun 11 2004
%D A013642 Kenneth H. Rosen, Elementary Number Theory and Its Applications, Addison-Wesley, 
               1984, page 426 (but beware of errors!)
%Y A013642 Cf. A001066 A043549 A026604 A047219 A090848 A004957.
%Y A013642 Sequence in context: A043549 A124051 A026604 this_sequence A140482 A118011 
               A047219
%Y A013642 Adjacent sequences: A013639 A013640 A013641 this_sequence A013643 A013644 
               A013645
%K A013642 nonn
%O A013642 1,1
%A A013642 Clark Kimberling (ck6(AT)evansville.edu)