319721821 has 4 divisors (see below), whose sum is σ = 319779612. Its totient is φ = 319664032.

The previous prime is 319721761. The next prime is 319721849. The reversal of 319721821 is 128127913.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 128127913 = 317 ⋅404189.

It can be written as a sum of positive squares in 2 ways, for example, as 251064025 + 68657796 = 15845^2 + 8286^2 .

It is a cyclic number.

It is not a de Polignac number, because 319721821 - 2⁹ = 319721309 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (319721851) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 19600 + ... + 31993.

It is an arithmetic number, because the mean of its divisors is an integer number (79944903).

Almost surely, 2^319721821 is an apocalyptic number.

It is an amenable number.

319721821 is a deficient number, since it is larger than the sum of its proper divisors (57791).

319721821 is an equidigital number, since it uses as much as digits as its factorization.

319721821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57790.

The product of its digits is 6048, while the sum is 34.

The square root of 319721821 is about 17880.7667900457. The cubic root of 319721821 is about 683.7921214611.

The spelling of 319721821 in words is "three hundred nineteen million, seven hundred twenty-one thousand, eight hundred twenty-one".