21388331 has 4 divisors (see below), whose sum is σ = 21966432. Its totient is φ = 20810232.

The previous prime is 21388327. The next prime is 21388333. The reversal of 21388331 is 13388312.

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

It is a cyclic number.

It is not a de Polignac number, because 21388331 - 2² = 21388327 is a prime.

It is a super-2 number, since 2×21388331² = 914921405931122, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21388294 and 21388303.

It is not an unprimeable number, because it can be changed into a prime (21388333) 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, 288995 + ... + 289068.

It is an arithmetic number, because the mean of its divisors is an integer number (5491608).

Almost surely, 2^21388331 is an apocalyptic number.

21388331 is a deficient number, since it is larger than the sum of its proper divisors (578101).

21388331 is an equidigital number, since it uses as much as digits as its factorization.

21388331 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 578100.

The product of its digits is 3456, while the sum is 29.

The square root of 21388331 is about 4624.7519933506. The cubic root of 21388331 is about 277.5826380510.

The spelling of 21388331 in words is "twenty-one million, three hundred eighty-eight thousand, three hundred thirty-one".