What is a simple formula for random number sequence?

I would like to have a function f(x) that gives good pseudo-random numbers in uniform distribution according to value x. I am aware of linear congruential generators, however these work in iterations, i.e. I provide the initial seed and then I get a sequence of random values one by one. This is not what I want, because if a want to get let's say 200000th number in the sequence, I have to compute numbers 1 ... 199999. I need a function that is given by one simple formula that uses basic operations such as +, *, mod, etc. I am also aware of hash functions but I didn't find any that suits these needs. I might come up with some function myself, but I'd like to use something that's been tested to give decent pseudo-random values. Is there anything like that being used?