21389431 has 12 divisors (see below), whose sum is σ = 25108272. Its totient is φ = 18166848.

The previous prime is 21389429. The next prime is 21389437. The reversal of 21389431 is 13498312.

It is not a de Polignac number, because 21389431 - 2¹ = 21389429 is a prime.

It is a super-2 number, since 2×21389431² = 915015517007522, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21389393 and 21389402.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21389437) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3606 + ... + 7468.

It is an arithmetic number, because the mean of its divisors is an integer number (2092356).

Almost surely, 2^21389431 is an apocalyptic number.

21389431 is a deficient number, since it is larger than the sum of its proper divisors (3718841).

21389431 is a wasteful number, since it uses less digits than its factorization.

21389431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3990 (or 3983 counting only the distinct ones).

The product of its digits is 5184, while the sum is 31.

The square root of 21389431 is about 4624.8709171176. The cubic root of 21389431 is about 277.5873966531.

The spelling of 21389431 in words is "twenty-one million, three hundred eighty-nine thousand, four hundred thirty-one".