21209999 has 12 divisors (see below), whose sum is σ = 22840800. Its totient is φ = 19688448.

The previous prime is 21209963. The next prime is 21210011. The reversal of 21209999 is 99990212.

It is not a de Polignac number, because 21209999 - 2⁸ = 21209743 is a prime.

It is a Duffinian number.

21209999 is a modest number, since divided by 9999 gives 2120 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21205999) 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 11 ways as a sum of consecutive naturals, for example, 22367 + ... + 23295.

It is an arithmetic number, because the mean of its divisors is an integer number (1903400).

Almost surely, 2^21209999 is an apocalyptic number.

21209999 is a deficient number, since it is larger than the sum of its proper divisors (1630801).

21209999 is an equidigital number, since it uses as much as digits as its factorization.

21209999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1042 (or 1025 counting only the distinct ones).

The product of its (nonzero) digits is 26244, while the sum is 41.

The square root of 21209999 is about 4605.4314673003. The cubic root of 21209999 is about 276.8090061263.

The spelling of 21209999 in words is "twenty-one million, two hundred nine thousand, nine hundred ninety-nine".