21309999 has 4 divisors (see below), whose sum is σ = 28413336. Its totient is φ = 14206664.

The previous prime is 21309997. The next prime is 21310007. The reversal of 21309999 is 99990312.

It is a happy number.

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 21309999 - 2¹ = 21309997 is a prime.

21309999 is a modest number, since divided by 9999 gives 2130 as remainder.

It is a self number, because there is not a number n which added to its sum of digits gives 21309999.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21309991) 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, 3551664 + ... + 3551669.

It is an arithmetic number, because the mean of its divisors is an integer number (7103334).

Almost surely, 2^21309999 is an apocalyptic number.

21309999 is a deficient number, since it is larger than the sum of its proper divisors (7103337).

21309999 is an equidigital number, since it uses as much as digits as its factorization.

21309999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7103336.

The product of its (nonzero) digits is 39366, while the sum is 42.

The square root of 21309999 is about 4616.2754467211. The cubic root of 21309999 is about 277.2433533304.

The spelling of 21309999 in words is "twenty-one million, three hundred nine thousand, nine hundred ninety-nine".