设这两个数为 x ,y,
满足 x + y > 51, 且 x < y
当 x =1 , 50 1
x =2, y=50 2
x=3, y=50,49,48, 3
x=4, y=50,...,47, 4
.....................
x=25,y=50,...,26 25
x=26,y=50,...,27 24
x=49,y=50 1
所以一共有 1+2 + 3+ ... 25 + 24+23+...+1
= 26*25/2 + 25*24/2
= 325 + 300
= 625