Fifty-three is the 16th prime number. It is the second balanced prime, and fifth isolated prime. 53 is a sexy prime with 47 and 59. It is the eighth Sophie Germain prime,[1] and the ninth Eisenstein prime.[2] The sum of the first 53 primes is 5830, which is divisible by 53, a property shared by only a few other numbers.[3][4] 53 cannot be expressed as the sum of any integer and its decimal digits, making 53 the ninth self number in decimal.[5] 53 is the smallest prime number that does not divide the order of any sporadic group, inclusive of the six pariahs; it is also the first prime number that is not a member of Bhargava's prime-universality criterion theorem (followed by the next prime number 59), an integer-matrix quadratic form that represents all prime numbers when it represents the sequence of seventeen integers {2, ..., 47, 67, 73}.[6] In hexadecimal, 53 is 35, that is, the same characters used in the decimal representation, but reversed. Four additional multiples of 53 share this property: 371 = 17316, 5141 = 141516, 99,481 = 1849916, and 8,520,280 = 082025816. Aside from the trivial single digit numbers, these are the only numbers that share this property.[7]
