You could also spawn off a number of threads and have each one pull the next item off the entire range. I.E. have a "next range item" variable and a mutex that protects it.

Each thread (in a loop until all values in the range are processed) locks the mutex, take the current value, increments it, unlock the mutex, and computes on the current value. This does create a hot spot at the mutex, but if the computation takes significantly long then I don't see that being a big deal.