21309869 has 16 divisors (see below), whose sum is σ = 25194240. Its totient is φ = 17646720.

The previous prime is 21309859. The next prime is 21309877. The reversal of 21309869 is 96890312.

It is not a de Polignac number, because 21309869 - 2²⁴ = 4532653 is a prime.

It is a super-2 number, since 2×21309869² = 908221033594322, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21309829) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 25937 + ... + 26745.

It is an arithmetic number, because the mean of its divisors is an integer number (1574640).

Almost surely, 2^21309869 is an apocalyptic number.

It is an amenable number.

21309869 is a deficient number, since it is larger than the sum of its proper divisors (3884371).

21309869 is an equidigital number, since it uses as much as digits as its factorization.

21309869 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 940.

The product of its (nonzero) digits is 23328, while the sum is 38.

The square root of 21309869 is about 4616.2613660840. The cubic root of 21309869 is about 277.2427895621.

The spelling of 21309869 in words is "twenty-one million, three hundred nine thousand, eight hundred sixty-nine".