27

This number is a composite.

+ The smallest 2-digit number in which the sum of digits is equal to the sum of prime factors (27 = 3 * 3 * 3 and 3 + 3 + 3 = 9). [Russo]

+ Vaughan (1977) showed that all integers are the sum of at most 27 prime numbers.

+ 2 and 7 are the smallest and largest single-digit primes.

+ 2 + 3 + 4 + 5 + 6 + 7 = 27. [Stone]

+ The product of the first 27 Mersenne prime exponents (minus one) is a 27 reversed-digit prime.

+ Smaller of the smallest pair of consecutive numbers with 3 prime factors. [Gupta]

+ The smallest number that is both a Smith number and a SPRP for a base less than one hundred. [H. Brown]

+ The smallest composite number n > 1 such that n! + 1 is prime. [Capelle]

+ π(2!!) * π(7!!) = 27. [Firoozbakht]

+ 27^27 + (2*7)^(2*7) is prime. [Silva]

+ π(27) = 2 + 7. [Kumar]

+ The smallest composite number which cannot be expressed as the sum of two primes. [Wesolowski]

+ The only prime cube that is one less than an even perfect number. [Gudipati]

+ The sum of all composite digits (4+6+8+9) equals the first odd prime cubed. [Silva]

(There are 9 curios for this number that have not yet been approved by an editor.)

Printed from the PrimePages <t5k.org> © G. L. Honaker and Chris K. Caldwell