21390375 has 16 divisors (see below), whose sum is σ = 35594208. Its totient is φ = 11408000.

The previous prime is 21390337. The next prime is 21390377. The reversal of 21390375 is 57309312.

It is not a de Polignac number, because 21390375 - 2⁷ = 21390247 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21390377) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 28146 + ... + 28895.

It is an arithmetic number, because the mean of its divisors is an integer number (2224638).

Almost surely, 2^21390375 is an apocalyptic number.

21390375 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21390375 is a deficient number, since it is larger than the sum of its proper divisors (14203833).

21390375 is an equidigital number, since it uses as much as digits as its factorization.

21390375 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 57059 (or 57049 counting only the distinct ones).

The product of its (nonzero) digits is 5670, while the sum is 30.

The square root of 21390375 is about 4624.9729728940. The cubic root of 21390375 is about 277.5914802688.

Adding to 21390375 its reverse (57309312), we get a palindrome (78699687).

The spelling of 21390375 in words is "twenty-one million, three hundred ninety thousand, three hundred seventy-five".