The file test1.in contains 1028 terms n*5^n-1. Sieving with:

  gcwsieve -i test1.in -p 1e5 -P 1e7

should find factors for 285 unique terms, including this special
case of one factor dividing two different terms:

  305329 | 19148*5^19148-1
  305329 | 18366*5^18366-1
