21000999 has 4 divisors (see below), whose sum is σ = 28001336. Its totient is φ = 14000664.

The previous prime is 21000983. The next prime is 21001021. The reversal of 21000999 is 99900012.

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

It is not a de Polignac number, because 21000999 - 2⁴ = 21000983 is a prime.

It is a Duffinian number.

21000999 is a modest number, since divided by 999 gives 21 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000599) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3500164 + ... + 3500169.

It is an arithmetic number, because the mean of its divisors is an integer number (7000334).

Almost surely, 2^21000999 is an apocalyptic number.

21000999 is a deficient number, since it is larger than the sum of its proper divisors (7000337).

21000999 is an equidigital number, since it uses as much as digits as its factorization.

21000999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7000336.

The product of its (nonzero) digits is 1458, while the sum is 30.

The square root of 21000999 is about 4582.6846934957. The cubic root of 21000999 is about 275.8967924342.

It can be divided in two parts, 2 and 1000999, that added together give a palindrome (1001001).

The spelling of 21000999 in words is "twenty-one million, nine hundred ninety-nine", and thus it is an aban number.