Sum of smallest non-trivial factors for a set of numbers

• reads in a positive integers in range (2 .. 2^63-1) from standard input
• initialize sum = 0
• for each number on input:
  • if the number is prime, it is ignored
  • determine the smallest factor of the composite number
  • add the smallest factor to a sum
• prints out the sum of all smallest factors

if no composite numbers are found, prints out “0”

compile with:

$ make

quick test:

$ echo "0 3 19 25 4012009 165 1033" | ./sumFactors 5
Using 5 threads.
Sum of divisors = 2011
$ echo "3 5" | ./sumFactors
Using 1 thread.
Sum of divisors = 0

Implemented in C++ with POSIX thread barriers. Multithreading is not easy at all, but this was quite fun to me.

Source code is available upon request.