The smallest three-digit prime Lucas number.
Adding it to 210n provides the smallest 8, 9, and 10 primes in arithmetic progression.
The smallest number with an additive persistence of 3. [Gupta]
The smallest prime that can be concatenated with the next prime in any order giving two primes: 199211 and 211199. [Gallardo]
The smallest prime that is the sum of the squares of four distinct primes. [Sladcik]
The X-15 aircraft made 199 flights. [McCranie]
199Hg (Mercury-199) is the heaviest stable atom which has a prime atomic weight. [Hartley]
(199, 211, 223) is the first triple of primes of the form (p, p+12, p+24). Note that for p < 1000 is the only such triple. Note also that 199211 and 223211 are primes. [Loungrides]
In 1941, Molsen proved that for n equal to or greater than 199, the interval n < p less than or equal to (8/7)n always contains a prime of each of the forms 3x+1, 3x-1. [Post]
The lesser of the smallest emirp pair (199, 991) each of whose members is the sum of a prime number of consecutive primes in a prime number of different ways: (199 = 61 + 67 + 71 = 31 + 37 + 41 + 43 + 47) ; (991 = 191 + 193 + 197 + 199 + 211 = 127 + 131 + 137 + 139 + 149 + 151 + 157). [Beedassy]
Largest known prime partial sum of Dedekind numbers. Equivalently partial sum of number of monotone Boolean functions of n variables, or partial sums of number of antichains of subsets of an n-set: 2 + 3 + 6 + 20 + 168 = 199 is prime. Curously, the first 5 such partial sums are prime (2, 5, 11, 31, 199), and then no more primes are known. [Post]
The smallest emirp formed from a double-digit number followed by the product of its digits. [Loungrides]
The smallest Lucas emirp. [Gudipati]
In visualizing the patterns generated in the "gaps of gaps" given by the prime numbers (e.g., below 199), a curious pattern emerges. This shows the gaps between the primes, followed by the absolute difference of those gaps, followed by the absolute difference of those gaps, etc., and on until all gaps are displayed in a (triangular) table of values. Done as a programming exercise, I was amazed to find patterns connecting common numbers in the table of gaps. Most interesting of these is the "dripping triangles" which reminds me of Wolfram diagrams. [Gene-Boggs]
The largest prime appearing on the Prime Numbers Activity chart by Math is Fun.
The smallest prime which is the sum of composite digits appearing in first primes up to itself. [Silva]
The smallest emirp p such that p and p^2 have the same sum of digits. [Gupta]
(There are 8 curios for this number that have not yet been approved by an editor.)