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19 Prime #1
Take nine pairs of numbers (a,b) where a+b=19. Take the sum a*b+19 for all of these nine pairs; ALL of the sums are primes. 19 is the LARGEST prime that will do this.
( $42 )





19 Prime #2
Pandigital palindromic primes start as 19digit numbers
( $42 )





19 Prime #3
(11, 13, 17, 19) is the first prime quadruple (p, q, r, s) such that s divides pqr+1.
( $42 )





19 Prime #4
There are exactly 19 primes between 2^5 1 and 2^71.
( $42 )





19 Prime #5
The last 19 digits of 17^18 are prime.
( $42 )








19 Prime #6
The only known prime of the form p*prime(p)^p + 1, where p is prime.
( $42 )





19 Prime #7
19 is the smallest prime which is the sum of three discrete composites (4 + 6 + 9).
( $42 )





19 Prime #8
19 is the only known prime of the form n^n  8. The next prime in this form (if it exists) will have more than 34000 digits.
( $42 )





19 Prime #9
Both numbers reversal (19!  1) and reversal ( 19! + 1) are primes. 19 is the largest known prime with this property.
( $42 )





19 Prime #10
The largest prime that is palindromic in Roman numerals alphabetically is XIX (19).
( $42 )








19 Prime #11
The first prime p such that p^2 is the reversal of a prime (163).
( $42 )





19 Prime #12
The following are primes: 19, 109, 1009, 10009. No other digit can replace the 9 and yield four primes.
( $42 )





19 Prime #13
19 is the only known number for which both (10^n1)/9 and (10^n+1)/11 are primes.
( $42 )





19 Prime #14
19 is the only prime p less than 30 that does not divide 30, where p + 30 is composite.
( $42 )





19 Prime #15
19 is the smallest prime with a digital root of 1.
( $42 )








19 Prime #16
19 is the smallest prime of the form 3p + 2q, where p and q are twin primes.
( $42 )





19 Prime #17
2^19  19 is prime.
( $42 )





19 Prime #18
19 is the smallest prime whose reversal is composite.
( $42 )





19 Prime #19 (o)
(19  1) divides (19^19  1) a prime number of times.
( $51 )




