A double factorial prime is a prime number of the form n!! ± 1, where n!! is a double factorial. n!! - 1 is prime for n = 3, 4, 6, 8, 16, 26, 64, 82, 90, 118, 194, 214, 728, ... (OEIS A007749), the largest of which are summarized in the following table. n!! - 1 | digits | discoverer 76190!! - 1 | 169, 435 | S. Fukai (Jun. 5, 2015) 100654!! - 1 | 229, 924 | S. Fukai (Jun. 5, 2015) 145706!! - 1 | 344, 538 | S. Fukai (Apr. 21, 2016) n!! + 1 is prime for n = 0, 1, 2, 518, 33416, 37310, 52608, 123998, ... (OEIS A080778), the largest of which are summarized in the following table.

double factorial | factorial prime | integer sequence primes | prime number