WinPFGW 3.8.3:
2^871991-4207 is 3-PRP! (339.2962s+0.0002s)
2^721721-4453 is 3-PRP! (220.0161s+0.0012s)
2^745039-4897 is 3-PRP! (252.2166s+0.0012s)

To be completed...