21811309 has 6 divisors (see below), whose sum is σ = 23618346. Its totient is φ = 20133360.

The previous prime is 21811261. The next prime is 21811351. The reversal of 21811309 is 90311812.

It can be written as a sum of positive squares in 3 ways, for example, as 605284 + 21206025 = 778^2 + 4605^2 .

It is not a de Polignac number, because 21811309 - 2²¹ = 19714157 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21811399) 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, 64362 + ... + 64699.

It is an arithmetic number, because the mean of its divisors is an integer number (3936391).

Almost surely, 2^21811309 is an apocalyptic number.

It is an amenable number.

21811309 is a deficient number, since it is larger than the sum of its proper divisors (1807037).

21811309 is a wasteful number, since it uses less digits than its factorization.

21811309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 129087 (or 129074 counting only the distinct ones).

The product of its (nonzero) digits is 432, while the sum is 25.

The square root of 21811309 is about 4670.2579157901. The cubic root of 21811309 is about 279.4005415009.

The spelling of 21811309 in words is "twenty-one million, eight hundred eleven thousand, three hundred nine".