>>20
Math Forum - Ask Dr. Math
いろいろやり方があるようです。
http://mathforum.org/library/drmath/view/56821.html
http://mathforum.org/library/drmath/view/61332.html
分母の和の値でありえるもの
http://www.research.att.com/~njas/sequences/A052428
解の例
(2,3,6) (2,3,7,42)(2,3,7,43,1806)(2,3,10,20,60)(2,3,12,15,60)(2,3,12,20,30)(2,4,5,21,420)
(2,4,5,22,220)(2,4,5,24,120)(2,4,5,25,100)(2,4,5,28,70)(2,4,5,30,60)(2,4,5,36,45)
(2,4,6,20,30)(2,4,6,15,60)(2,4,7,14,28) (2,4,8,12,24)(2,4,8,16,32,48,96)(2,4,10,12,15)
(2,6,8,12,16,24,48)(3,4,5,6,20)