The seventh challenge of the 2021 Series will be a 7-day challenge in celebration of the 107th (prime number!) birthday of beloved American science communicator, Martin Gardner. The challenge will be offered on the GCW-LLR application, beginning 21 October 00:00 UTC and ending 28 October 00:00 UTC. To participate in the Challenge, please select only the Generalized Cullen/Woodall Prime Search LLR (GCW) project in your PrimeGrid preferences section. For more info and discussion, check out the forum thread for this challenge: https://www.primegrid.com/forum_thread.php?id=9767&nowrap=true#151803 Best of luck!

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