818921 has 4 divisors (see below), whose sum is σ = 841092. Its totient is φ = 796752.

The previous prime is 818897. The next prime is 818947. The reversal of 818921 is 129818.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 583696 + 235225 = 764^2 + 485^2 .

It is a cyclic number.

It is not a de Polignac number, because 818921 - 2¹⁰ = 817897 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a plaindrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (818021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11030 + ... + 11103.

It is an arithmetic number, because the mean of its divisors is an integer number (210273).

2⁸¹⁸⁹²¹ is an apocalyptic number.

It is an amenable number.

818921 is a deficient number, since it is larger than the sum of its proper divisors (22171).

818921 is a wasteful number, since it uses less digits than its factorization.

818921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22170.

The product of its digits is 1152, while the sum is 29.

The square root of 818921 is about 904.9425396123. The cubic root of 818921 is about 93.5579440085.

It can be divided in two parts, 818 and 921, that multiplied together give a triangular number (753378 = T₁₂₂₇).

The spelling of 818921 in words is "eight hundred eighteen thousand, nine hundred twenty-one".