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Double Factorial Prime


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!!-1digitsdiscoverer
76190!!-1169,435S. Fukai (Jun. 5, 2015)
100654!!-1229,924S. Fukai (Jun. 5, 2015)
145706!!-1344,538S. 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.

n!!+1digitsdiscoverer
52608!!+1112,762H. Jamke (Jan. 3, 2008)
123998!!+1288,864S. Fukai (Jun. 5, 2015)

See also

Double Factorial, Factorial Prime, Integer Sequence Primes, Prime Number

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References

Sloane, N. J. A. Sequences A007749 and A080778 in "The On-Line Encyclopedia of Integer Sequences."

Cite this as:

Weisstein, Eric W. "Double Factorial Prime." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/DoubleFactorialPrime.html

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