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A256694
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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.
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2
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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;
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listen;
history;
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internal format)
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..52.
Kival Ngaokrajang, Illustration of the first three solutions
Eric Weisstein's World of Mathematics, Soddy Circles.
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PROG
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(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)
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CROSSREFS
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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
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KEYWORD
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nonn
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AUTHOR
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Colin Barker, Apr 08 2015
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STATUS
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approved
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