exponential in dependency formula

I created my characteristics where the user will input:

Purchaseprice

Salvagevalue

Leasefactor (which is input as 0.0000%)

and Economiclife.

I'm trying to get my procedure for the formula to match what the formula in excel gives me. What I have is:

$self.leaseamount =

((($self.purchaseprice(1+$self.factor/12)^($self.economiclife12))-

($self.purchaseprice*$self.salvagevalue)) /

(((1+self.factor/12)^($self.economiclife*12)-1)/(self.factor/12))

It doesn't seem to like that '^' - so in SAP what do you use for exponential? Please help.

Thanks

Karla