19
This number is a prime.
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19 is the smallest prime p such that 10*p {+ 1, 3, 7, and 9} are all primes. [Das]
The first prime repfigit number. A repfigit (repetitive fibonacci-like digit) number is an n-digit integer N with the following property: if a Fibonacci-like sequence (in which each term in the sequence is the sum of the n previous terms) is formed, with the first n terms being the decimal digits of the number N, then N itself occurs as a term in the sequence. For example, if the digits of 19 start a Fibonacci-like sequence, then 19 appears as a term: 1, 9, 10, 19. These are also known as Keith numbers. [Beedassy]
The largest prime that is palindromic in Roman numerals alphabetically is XIX (19). [Beedassy]
19 is the "age of
majority" adopted under federal jurisdiction in two US
states, viz., Nebraska, Alabama. [Beedassy]
The index p of the largest known Mersenne prime
Mp = 2p - 1
having an associated perfect number
Mp*2p - 1 that
is short of a prime by 1. [Beedassy]
The number of topologically distinct planar
configurations without discontinuities that are
possible using six matches. [Beedassy]
The number of letters in the anagrammatic title "A Superb
Mosaic - Dare it !" that fittingly qualifies the "PRIME
CURIOS DATABASE" with a poetic touch. [Beedassy]
Pandigital palindromic primes
start as 19-digit numbers. [Beedassy]