Attached are four simple solvers.

The first three consist of a serial Python script that can generate roughly the first 17,000 repunits in 60 seconds, a serial C program that can generate about 120,000 repunits in 60 seconds, and a naive, parallel, MPI C program that, on an Intel Core i7 processor and running with 16 threads, can calculate about 190,000 repunits in 60 seconds.

The final solver makes use of the constant nature of the memcpy() function in C and appends an additional 1 to the end of each previous repunit to form a new repunit. Although this means that after each repunit is generated, it can only be accessed until the following term is created, this method can generate over 1,000,000 terms in 60 seconds if executed serially.

You should use these as benchmarks for your own program.