Hi Andy,
If you give it a certain seed value you'll get a certain "random" sequence of number and that sequency will be the same every time you give it that particular seed value. Mutliplying any seed value by a constant number (prime or not) will only result in a sequence of number like if you've given it that particular seed number from the beginning - it won't make it more random. It may even be so (easy to check) that the seed value is actually only a pointer into the sequence of numbers, ie where to start in the static sequence of "random" numbers.

For something like a dice whice involves human interactin you have the best "random" generator available in the form of time. Let a timer free run and just grab its value when a new number is needed. There's no way a user is going to be able to "pick" a certain number.

/Henrik.