21399875 has 32 divisors (see below), whose sum is σ = 31394688. Its totient is φ = 14256000.

The previous prime is 21399839. The next prime is 21399901. The reversal of 21399875 is 57899312.

It is a Cunningham number, because it is equal to 4626²-1.

It is not a de Polignac number, because 21399875 - 2¹⁸ = 21137731 is a prime.

It is a Duffinian number.

Its product of digits (136080) is a multiple of the sum of its prime factors (720).

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 32045 + ... + 32705.

It is an arithmetic number, because the mean of its divisors is an integer number (981084).

Almost surely, 2^21399875 is an apocalyptic number.

21399875 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21399875 is a deficient number, since it is larger than the sum of its proper divisors (9994813).

21399875 is an equidigital number, since it uses as much as digits as its factorization.

21399875 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 720 (or 710 counting only the distinct ones).

The product of its digits is 136080, while the sum is 44.

The square root of 21399875 is about 4625.9998919153. Note that the first 3 decimals coincide. The cubic root of 21399875 is about 277.6325692906.

The spelling of 21399875 in words is "twenty-one million, three hundred ninety-nine thousand, eight hundred seventy-five".