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 A256694 The radius of the largest of four circles with different integer radii arranged so that each circle is tangent externally to the other three circles. 2
 69, 70, 132, 138, 140, 153, 198, 207, 210, 216, 238, 252, 264, 264, 264, 270, 276, 280, 285, 290, 306, 345, 350, 390, 396, 396, 414, 420, 429, 432, 459, 476, 483, 490, 504, 504, 520, 528, 528, 528, 539, 540, 552, 560, 567, 570, 580, 594, 595, 612, 621, 630 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Kival Ngaokrajang, Illustration of the first three solutions Eric Weisstein's World of Mathematics, Soddy Circles. PROG (PARI) soddy(k) = {   s=[];   for(a=1, k,     for(b=1, a-1,       for(c=1, b-1,         if(issquare(a*b*c*(a+b+c), &t),           if(a*b*c % (a*b+a*c+b*c+2*t) == 0,             s=concat(s, a)           )         )       )     )   );   s } soddy(500) CROSSREFS See also the many sequences arising from Apollonian circle packing: A135849, A137246, A154636, etc. Also the sequences related to Soddy's circle packings: A046159, A046160, A062536, etc. Sequence in context: A265189 A345486 A253430 * A166067 A253437 A325386 Adjacent sequences:  A256691 A256692 A256693 * A256695 A256696 A256697 KEYWORD nonn AUTHOR Colin Barker, Apr 08 2015 STATUS approved

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Last modified August 10 06:08 EDT 2022. Contains 356029 sequences. (Running on oeis4.)