Making BIG calculations with vb.net(75+ digits)

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VB

mathematics

SOLVED
Thx SAKryukov[^]

Hey there! I need to make some BIG calculations using binomial coefficients[^]

Ok, since vb.net doesn't have factorial nor binomial coefficient functions I've already done my own:

Function fact(ByVal Number As Byte) As Decimal
        Dim i As Integer = 1
        Dim Calculated As Decimal = 0

        Calculated = Number

        Do While i < Number
            Calculated *= (Number - i)
            i += 1
        Loop

        Return Calculated
    End Function

    Function C(ByVal n As Byte, ByVal p As Byte) As Decimal
        Return ((fact(n)) / (fact(p) * fact(n - p)))
    End Function

But here is my problem, I need to make calculations with numbers bigger then the biggest binomial using a byte as n and as p and that is:
(ps: I know that a byte is only up to 255, but I'm shifting it up one unit, so 0 is 1.....and 255 would be 256)

C(256, 128) = 5768658823449206338089748357862286887740211701975162032608436567264518750790

Or have a look Here
And that has 75 digits, the BIGGEST data type vb.net has is decimal with 28 digits.

Does anyone know how I can work around this?