OFFSET
1,1
FORMULA
Squared radius of circumcircle of triangle with sides a, b, c:
R^2 = (a*b*c)^2 / (16*s*(s - a)*(s - b)*(s - c)) with s = (a + b + c)/2.
EXAMPLE
a(1) = 3, because the triangle with sides (3,3,3) is the first triangle for which R^2 has an integer value.
a(2) = 12: (6,6,6),
a(3) = 25: (6,8,10) scaled-up Pythagorean triangle (3,4,5),
a(4) = 27: (9,9,9),
a(5) = 48: (12,12,12),
...
a(10) = 147: (9,15,21).
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Hugo Pfoertner, Jan 13 2020
STATUS
approved