OFFSET
1,1
COMMENTS
Any number a(n) is also a hypotenuse number A009003 (and conversely) - see Pahikkala 2010, Theorem 5.
LINKS
Jussi Pahikkala, On contraharmonic mean and Pythagorean triples, Elemente der Mathematik, 65:2 (2010), 62-67.
PlanetMath, Contraharmonic proportion
PlanetMath, Integer contraharmonic means [From Pahikkala Jussi, Sep 05 2010]
FORMULA
The contraharmonic mean of u and v is (u^2+v^2)/(u+v).
EXAMPLE
a(1) = (2^2+6^2)/(2+6) = 5, a(2) = (3^2+6^2)/(3+6) = 5, a(3) = (3^2+15^2)/(3+15) = 13.
MAPLE
K:=100; t1:=[];
for u from 1 to K-1 do for v from u+1 to 2*u^2-u do
if (u^2+v^2) mod (u+v) = 0 then t1:=[op(t1), (u^2+v^2)/(u+v)]; fi;
od: od: t1; # N. J. A. Sloane, Mar 20 2011
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Pahikkala Jussi, Nov 04 2008
EXTENSIONS
Minor edits by N. J. A. Sloane, Mar 20 2011
STATUS
approved