21408375 has 16 divisors (see below), whose sum is σ = 35624160. Its totient is φ = 11417600.

The previous prime is 21408353. The next prime is 21408397. The reversal of 21408375 is 57380412.

It is an interprime number because it is at equal distance from previous prime (21408353) and next prime (21408397).

It is not a de Polignac number, because 21408375 - 2¹⁸ = 21146231 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 28170 + ... + 28919.

It is an arithmetic number, because the mean of its divisors is an integer number (2226510).

Almost surely, 2^21408375 is an apocalyptic number.

21408375 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21408375 is a deficient number, since it is larger than the sum of its proper divisors (14215785).

21408375 is an equidigital number, since it uses as much as digits as its factorization.

21408375 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57107 (or 57097 counting only the distinct ones).

The product of its (nonzero) digits is 6720, while the sum is 30.

The square root of 21408375 is about 4626.9185210029. The cubic root of 21408375 is about 277.6693228458.

Adding to 21408375 its reverse (57380412), we get a palindrome (78788787).

The spelling of 21408375 in words is "twenty-one million, four hundred eight thousand, three hundred seventy-five".