Largest known alternating factorial prime

The largest known alternating factorial prime is equal to a(661), which is 1,579 digits long; it has been discovered in July 2000.Alternating Factorial -- from Wolfram MathWorld
The largest known alternating factorial probable prime is equal to a(59,961), which is 260,448 digits long; it has been discovered on September 18, 2017.
== Sources ==
Category:Numbers
Category:Class 2
Category:Factorial numbers
Category:Numbers with 1000 to 1000000 digits
Category:Numerical records
Category:Prime numbers
Category:Probable primes
Category:Dynamic googolisms