Thread: "Rare" Primes
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Old 2008-08-19, 19:34   #1
Housemouse
 
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Feb 2008

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Default "Rare" Primes

I am looking for "rare" prime numbers. For purposes of this tread a prime number is rare if there are 10 or less known examples. Even if it is believed that there is an infinate number of primes of a partiocular type; it is rare if there are 10 or less known examples.

Even primes n
n=2

Generalized Fermat 10^2^n+1
n=1

Subfactorial !n
n=2

Perfect number -1; n is a perfect number
n=6

Sequential prime of type (1234567890)n1
n=17, 56

Subfactorial +1; !n+1
n=2, 3

Type: n^n^n +1
n=1, 2

Wilson primes; (n-1)!+1 is divisible by n^2

Subfactorial - 1; !n-1
n= 5, 15, 17

Type: n^n+1
n=1, 2, 4

Double Mersenne; 2^n-1; where n is a Mersenne prime
n=2, 3, 5, 7

Perfect number +1; where n is a perfect number
n= 6, 28, 496, 137,438,691,328

Fermat prime; 2^n+1
n=0, 1, 2, 3, 4

Repunit containing only decimal digit 1; n= number of digits
n=2, 19, 23, 317, 1,031
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