21309889 has 6 divisors (see below), whose sum is σ = 21533270. Its totient is φ = 21088800.

The previous prime is 21309877. The next prime is 21309907. The reversal of 21309889 is 98890312.

It can be written as a sum of positive squares in 3 ways, for example, as 18447025 + 2862864 = 4295^2 + 1692^2 .

It is not a de Polignac number, because 21309889 - 2¹¹ = 21307841 is a prime.

It is a super-2 number, since 2×21309889² = 908222738384642, which contains 22 as substring.

It is a Duffinian 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 5 ways as a sum of consecutive naturals, for example, 9157 + ... + 11245.

Almost surely, 2^21309889 is an apocalyptic number.

It is an amenable number.

21309889 is a deficient number, since it is larger than the sum of its proper divisors (223381).

21309889 is an equidigital number, since it uses as much as digits as its factorization.

21309889 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2291 (or 2190 counting only the distinct ones).

The product of its (nonzero) digits is 31104, while the sum is 40.

The square root of 21309889 is about 4616.2635323387. The cubic root of 21309889 is about 277.2428762958.

The spelling of 21309889 in words is "twenty-one million, three hundred nine thousand, eight hundred eighty-nine".