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.

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

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 A357614 A096840

Adjacent sequences: A280677 A280678 A280679 * A280681 A280682 A280683

Keyword

nonn,tabf

Author

Colin Barker, Jan 07 2017

Status

approved