197

This number is a prime.

+ The only three-digit prime repfigit number. [Trotter]

+ 197 and 2197 * 197# - 1 are primes. [Boland]

+ The first three digits of the prime 197 * 197! + 1 are 197. [Luhn]

+ Surrey and England batsman Jack Hobbs scored a record 197 centuries.

+ The sum of the first dozen primes. [Brod]

+ The smallest prime number that is the sum of 7 consecutive prime numbers (17+19+23+29+31+37+41). [Schuler]

+ 197 is the sum of digits of all two-digit primes. [Gallardo]

+ The smallest multidigit prime p that makes 10^p-9 prime. Note that the next prime (199) has the same property. They are twin primes! [Gallardo]

+ This prime is the smallest number to be the sum of repdigits of its digits: 111 + 9 + 77 = 197. [Post]

+ The sum of the squares of all the four composite digits (4^2 + 6^2 + 8^2 + 9^2). [Silva]

+ The digits contained in two-digit primes under 100, up to 97, sum to 100+97. [Silva]

+ If A=1, B=2, C=3, … , Z=26 then 'A PRIME QUADRUPLET' is one of four primes in a prime quadruplet. [Homewood]

+ 19 x 7 + (1 x 9 x 7) + 1 = 197. [Homewood]

+ A self-referential (or auto-descriptive) sentence due to Lee Sallows consists of a prime number of letters: "This sentence contains one hundred and ninety-seven letters: four a’s, one b, three c’s, five d’s, thirty-four e’s, seven f’s, one g, six h’s, twelve i’s, three l’s, twenty-six n’s, ten o’s, ten r’s, twenty-nine s’s, nineteen t’s, six u’s, seven v’s, four w’s, four x’s, five y’s, and one z." [Beedassy]

+ |8*k^2 + 8*k − 197| generates only primes for k = 0 to 30. [Yosei]

+ 197 is a Russian Doll prime as 197, 97 and 7 are primes. [Buchanon]

(There are 2 curios for this number that have not yet been approved by an editor.)

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