This example shows how PLINQ can be used to calculate the even numbers between 1 and 10,000 using multiple threads. Note that the resulting list will won't be ordered!
var sequence = Enumerable.Range(1, 10000);
var evenNumbers = sequence.AsParallel()
.Where(x => x % 2 == 0)
.ToList();
// evenNumbers = { 4, 26, 28, 30, ... }
// Order will vary with different runs