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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
OFFSET
1,1
LINKS
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
KEYWORD
nonn
AUTHOR
Colin Barker, Apr 08 2015
STATUS
approved