The way pseudorandom numbers generally work is to modify the seed according to some formula then use the new value as the next seed. So:
initialise seed <- this is the number you enter
random number = f(seed) <- this function returns a random number as a function of seed
random number 2 = f(random number) <- so the result of the previous is fed into the function again.
So you need to keep seed somewhere instead of discarding it, so I would suggest making the "please enter" part a separate part of randnum[ber]() and pass the seed into this function.
A for loop will do the "display 10 random numbers" bit.