<P> 73 is: </P> <Ul> <Li> the 21st prime number . The previous is seventy - one, with which it comprises the 8th twin prime . </Li> <Li> a permutable prime with thirty - seven . </Li> <Li> a star number . </Li> <Li> the largest minimal Primitive root in the first 100,000 primes . In other words, if p is one of the first 100,000 primes, then at least one of the primes 3, 5, 7, 11, 13, 17,..., 73 is a primitive root modulo p . </Li> <Li> the smallest prime congruent to 1 modulo 24 . </Li> <Li> an emirp, meaning that the reverse of 73, that is, 37, is also a prime number . 73 is the 21st prime number while 37 is the 12th prime number . </Li> <Li> the smallest prime with a composite sum of digits, in base 5 . </Li> <Li> palindromic in bases 2 (1001001) and 8 (111). </Li> <Li> 73 is the only prime repunit in base 8 (111). </Li> <Li> 73 is the smallest factor of the first composite generalized Fermat number in base 10 (10 + 1 = 10,001 = 73 × 137). </Li> </Ul> <Li> the 21st prime number . The previous is seventy - one, with which it comprises the 8th twin prime . </Li> <Li> a permutable prime with thirty - seven . </Li>

Which is the best number in the world