Hi,
Just made this function. You can use it if you are only interested in x^n
(mod M) and not x^n. The formula is a so-called recursive that calls itself
N times. The trick is to calculate the Modulus before calculating the next
step. I have no mathematical proof that is is correct (I'm not
mathematician), but I tested it on different calculations and saw no
difference from "=MOD(X^N;M)". Like feed-back if anyone thinks that the
function has any flaws.

rgds,
Lazzzx

Function ExpMod(X As Long, N As Long, M As Long) As Long
Static R As Long
If R = 0 Then R = 1
If N 0 Then R = (R Mod M) * X * ExpMod(X, N - 1, M)
ExpMod = R Mod M
R = 1
End Function



"Diogo" skrev i meddelelsen
...
Need to calculate via Excel:

mod(13^271;162653)

Any thoughts????

Thanks