1*2*3+2*3*4+3*4*5+.n*(n+1)*(n+2)+...计算输出下面级数前n项(n=20)的部分和,

Private Sub Command1_Click()
Dim n%,i%,y%,a%
a = 0
y = 1
n = Val(text1.Text)
For i = 1 To n
a = a + 1
y = y * a
Next i
End Su