请问怎么用总数分配随机数到固定天数

Option Explicit
Sub abc()
　Dim a, i, j, m, n, t
　ReDim a(1 To 1617) '报告单总数
　For i = 1 To UBound(a)
　　a(i) = i
　Next
　For i = 1 To UBound(a)
　　n = Int(Rnd * UBound(a)) + 1
　　t = a(i): a(i) = a(n): a(n) = t
　Next
　n = 30 '指定月天数
　If n < 28 Or n > 31 Then MsgBox "!": Exit Sub
　ReDim b(1 To n, 1 To UBound(a) \ n + 1)
　For i = 1 To UBound(a) Step UBound(a) \ n
　　m = m + 1
　　For j = i To i + UBound(a) \ n - 1
　　　b(m, j - i + 1) = a(j)
　　Next
　　If m = UBound(b) Then Exit For
　Next
　m = 0
　For i = UBound(a) - (UBound(a) Mod n) + 1 To UBound(a)
　　m = m + 1
　　b(m, UBound(b, 2)) = a(i)
　Next
　[a1].Resize(UBound(b), UBound(b, 2)) = b
End Sub