813 has 4 divisors (see below), whose sum is σ = 1088.
Its totient is φ = 540.
The previous prime is 811. The next prime is 821. The reversal of 813 is 318.
813 is nontrivially palindromic in base 15.
It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.
It is not a de Polignac number, because 813 - 21 = 811 is a prime.
It is a D-number.
It is the 29-th Hogben number.
It is a Duffinian number.
813 is an undulating number in base 15.
It is a Curzon number.
It is a plaindrome in base 5, base 8, base 11 and base 12.
It is a nialpdrome in base 14.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (811) by changing a digit.
It is a nontrivial repunit in base 28.
It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 133 + ... + 138.
It is an arithmetic number, because the mean of its divisors is an integer number (272).
It is an amenable number.
813 is a deficient number, since it is larger than the sum of its proper divisors (275).
813 is a wasteful number, since it uses less digits than its factorization.
813 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 274.
The product of its digits is 24, while the sum is 12.
The square root of 813 is about 28.5131548588.
The cubic root of 813 is about 9.3331916078.
Note that the first 3 decimals are identical.
It can be divided in two parts, 81 and 3, that multiplied together give a 5-th power (243 = 35).
The spelling of 813 in words is "eight hundred thirteen", and thus it is an aban number and an oban number.