21031999 has 4 divisors (see below), whose sum is σ = 21098664. Its totient is φ = 20965336.

The previous prime is 21031979. The next prime is 21032003. The reversal of 21031999 is 99913012.

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 21031999 - 2⁹ = 21031487 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 (21031909) 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, 32857 + ... + 33490.

It is an arithmetic number, because the mean of its divisors is an integer number (5274666).

Almost surely, 2^21031999 is an apocalyptic number.

21031999 is a deficient number, since it is larger than the sum of its proper divisors (66665).

21031999 is an equidigital number, since it uses as much as digits as its factorization.

21031999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 66664.

The product of its (nonzero) digits is 4374, while the sum is 34.

The square root of 21031999 is about 4586.0657430961. The cubic root of 21031999 is about 276.0324779746.

The spelling of 21031999 in words is "twenty-one million, thirty-one thousand, nine hundred ninety-nine".