12391821 has 12 divisors (see below), whose sum is σ = 19276348. Its totient is φ = 7625664.

The previous prime is 12391811. The next prime is 12391831. The reversal of 12391821 is 12819321.

12391821 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (12391811) and next prime (12391831).

It can be written as a sum of positive squares in 2 ways, for example, as 4473225 + 7918596 = 2115^2 + 2814^2 .

It is not a de Polignac number, because 12391821 - 2⁵ = 12391789 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (12391811) 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 11 ways as a sum of consecutive naturals, for example, 52840 + ... + 53073.

Almost surely, 2^12391821 is an apocalyptic number.

It is an amenable number.

12391821 is a deficient number, since it is larger than the sum of its proper divisors (6884527).

12391821 is a wasteful number, since it uses less digits than its factorization.

12391821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 105932 (or 105929 counting only the distinct ones).

The product of its digits is 864, while the sum is 27.

The square root of 12391821 is about 3520.2018408040. The cubic root of 12391821 is about 231.4080044104.

The spelling of 12391821 in words is "twelve million, three hundred ninety-one thousand, eight hundred twenty-one".