21055999 has 4 divisors (see below), whose sum is σ = 21453336. Its totient is φ = 20658664.

The previous prime is 21055967. The next prime is 21056011. The reversal of 21055999 is 99955012.

21055999 = 282² + 283² + ... + 440².

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21055999 - 2⁵ = 21055967 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21055399) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 198589 + ... + 198694.

It is an arithmetic number, because the mean of its divisors is an integer number (5363334).

Almost surely, 2^21055999 is an apocalyptic number.

21055999 is a deficient number, since it is larger than the sum of its proper divisors (397337).

21055999 is an equidigital number, since it uses as much as digits as its factorization.

21055999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 397336.

The product of its (nonzero) digits is 36450, while the sum is 40.

The square root of 21055999 is about 4588.6816189402. The cubic root of 21055999 is about 276.1374333045.

The spelling of 21055999 in words is "twenty-one million, fifty-five thousand, nine hundred ninety-nine".