Factorial of large numbers

Public Function factorial (intc as integer) as string
On Error goto myerr:
Dim INTA () as integer, intt () as integer, I as integer
Dim J as integer, Intr as integer
Redim INTA (20), intt (20)
If intc <2 then exit function
Intr = 20
INTA (0) = 1
For I = 2 to intc
For J = 0 to intr
Intt (j) = INTA (j) * I
Next J
J = 0
Do until j> intr
INTA (j) = intt (j) mod 10
If intt (j)> = 10 then intt (J + 1) = intt (J + 1) + intt (j)/10
J = J + 1
Loop
Next I

Do While true
J = J-1
If INTA (j)> 0 Then exit do
Loop

For J = J to 0 step-1
Factorial = factorial & INTA (j)
Next J
Exit Function
Myerr:
If err. Number = 9 then
Intr = intr + 20
Redim preserve INTA (intr)
Redim preserve intt (intr)
Resume
Else
Msgbox "unknow err:" & err. Description & ":" & err. Number, vbcritical + vbokonly
End if
End Function