Hi, i've written a programme to decrypt rsa and it works fine for small values, for example when i chose my two primes to be 3 and 7 and therefore n=3*7=21 and totient function=12.

But i have to decrypt rsa with much larger primes, 167 and 233. So n=38911, totient function =38512
This means i have to calculate 18^8423 (mod(38911))!!
which is way too big for my computer to remember, isn't it?

i'm using double variables, what kind of variables would allow me to do this calculation?