对非负整数N,满足X+Y+2Z=N的非负整数解（X,Y,Z）的组数记为An,求A3的值

题目

对非负整数N,满足X+Y+2Z=N的非负整数解（X,Y,Z）的组数记为An,求A3的值

答案

(1,0,1)
(0,1,1)
(2,1,0)
(1,2,0)
(3,0,0)
(0,3,0)
所以A3＝6