21387231 has 6 divisors (see below), whose sum is σ = 30892680. Its totient is φ = 14258148.

The previous prime is 21387227. The next prime is 21387251. The reversal of 21387231 is 13278312.

It is not a de Polignac number, because 21387231 - 2² = 21387227 is a prime.

It is a super-2 number, since 2×21387231² = 914827299694722, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21387195 and 21387204.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21387251) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1188171 + ... + 1188188.

It is an arithmetic number, because the mean of its divisors is an integer number (5148780).

Almost surely, 2^21387231 is an apocalyptic number.

21387231 is a deficient number, since it is larger than the sum of its proper divisors (9505449).

21387231 is a wasteful number, since it uses less digits than its factorization.

21387231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2376365 (or 2376362 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 21387231 is about 4624.6330665254. The cubic root of 21387231 is about 277.5778792858.

The spelling of 21387231 in words is "twenty-one million, three hundred eighty-seven thousand, two hundred thirty-one".