33

This number is a composite.

+ The number of primes and the number of semiprimes up to 33 are equal. [Gupta]

+ The smallest run of 3 consecutive integers that are semi-primes (the product of two primes) begins with 33. [Wells]

+ The smallest palindromic number n such that inserting a digit '1' between adjacent digits of n is prime. [Russo]

+ First exponent to yield 3 generalized cullen primes: 33*4^33+1, 33*14^33+1 and 33*34^33+1 [Chun Wa]

+ The smallest triadic semiprime. [Capelle]

+ The largest known number (coincidentally semiprime) that is not the sum of two semiprimes. [Capelle]

+ The largest integer n such that π(n) = n/3. [Bajpai]

+ The smallest odd number n such that n+x! is not a prime, for any number x. [Loungrides]

(There are 3 curios for this number that have not yet been approved by an editor.)

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