21056399 has 16 divisors (see below), whose sum is σ = 26288640. Its totient is φ = 16420320.

The previous prime is 21056381. The next prime is 21056401. The reversal of 21056399 is 99365012.

It is not a de Polignac number, because 21056399 - 2⁸ = 21056143 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21056699) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4832 + ... + 8090.

It is an arithmetic number, because the mean of its divisors is an integer number (1643040).

Almost surely, 2^21056399 is an apocalyptic number.

21056399 is a deficient number, since it is larger than the sum of its proper divisors (5232241).

21056399 is a wasteful number, since it uses less digits than its factorization.

21056399 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3350.

The product of its (nonzero) digits is 14580, while the sum is 35.

The square root of 21056399 is about 4588.7252042370. The cubic root of 21056399 is about 276.1391818842.

The spelling of 21056399 in words is "twenty-one million, fifty-six thousand, three hundred ninety-nine".