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 A280680 The square roots of the radii (a, b, c) of three primitive mutually tangent circles all touching the same straight line, with a > b > c. 2
 6, 3, 2, 12, 4, 3, 15, 10, 6, 20, 5, 4, 28, 21, 12, 30, 6, 5, 35, 14, 10, 40, 24, 15, 42, 7, 6, 45, 36, 20, 56, 8, 7, 63, 18, 14, 66, 55, 30, 70, 30, 21, 72, 9, 8, 77, 44, 28, 84, 60, 35, 88, 33, 24, 90, 10, 9, 91, 78, 42, 99, 22, 18, 104, 65, 40 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Colin Barker, Table of n, a(n) for n = 1..3000 Eric Weisstein's World of Mathematics, Tangent Circles EXAMPLE The first few triples are [6, 3, 2], [12, 4, 3], [15, 10, 6], [20, 5, 4]. PROG (PARI) a280680(amax) = {   my(L=List());   for(a=1, amax,     for(b=1, a-1,       c=(1/(1/a + 1/b))^2;       if(type(c)=="t_INT" && gcd([a^2, b^2, c])==1,         listput(L, [a, b, sqrtint(c)])       )     )   );   Vec(L) } concat(a280680(100)) CROSSREFS Cf. A106430, A246429, A247372, A265189, A280679. Sequence in context: A011488 A021162 A114348 * A272083 A096840 A096685 Adjacent sequences:  A280677 A280678 A280679 * A280681 A280682 A280683 KEYWORD nonn,tabf AUTHOR Colin Barker, Jan 07 2017 STATUS approved

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Last modified April 6 08:27 EDT 2020. Contains 333268 sequences. (Running on oeis4.)