A089059 - OEIS

%I #4 Oct 01 2013 17:57:46

%S 21,42,63,84,85,105,126,147,168,170,184,189,210,217,231,252,255,273,

%T 294,315,336,340,357,368,378,399,420,425,434,441,441,462,483

%N Numbers x such that xy/(x+y) is an integer and the hypotenuse of the right triangle with legs x and y is an integer.

%C These numbers are almost always divisible by 7. 85 in the example is an exception and so is 184.

%e x=85,y=204, 85^2+204^2 = 221^2

%o (PARI) xydivxpy2(n) = { for(x=1, n, for(y=x, n, h=x*y/(x+y); if(h==floor(h), z = sqrt (x^2+y^2); if(z==floor(z), print1(x", ") ) ) ) ) }

%K nonn

%O 1,1

%A _Cino Hilliard_, Dec 02 2003, corrected Nov 23 2006