21255391 has 4 divisors (see below), whose sum is σ = 21266784. Its totient is φ = 21244000.

The previous prime is 21255383. The next prime is 21255401. The reversal of 21255391 is 19355212.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21255391 - 2³ = 21255383 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21255301) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2170 + ... + 6871.

It is an arithmetic number, because the mean of its divisors is an integer number (5316696).

Almost surely, 2^21255391 is an apocalyptic number.

21255391 is a deficient number, since it is larger than the sum of its proper divisors (11393).

21255391 is an equidigital number, since it uses as much as digits as its factorization.

21255391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11392.

The product of its digits is 2700, while the sum is 28.

The square root of 21255391 is about 4610.3569276142. The cubic root of 21255391 is about 277.0063338358.

The spelling of 21255391 in words is "twenty-one million, two hundred fifty-five thousand, three hundred ninety-one".