21831309 has 16 divisors (see below), whose sum is σ = 32415040. Its totient is φ = 14521680.

The previous prime is 21831263. The next prime is 21831353. The reversal of 21831309 is 90313812.

It is not a de Polignac number, because 21831309 - 2⁷ = 21831181 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21835309) 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 15 ways as a sum of consecutive naturals, for example, 21399 + ... + 22395.

It is an arithmetic number, because the mean of its divisors is an integer number (2025940).

Almost surely, 2^21831309 is an apocalyptic number.

It is an amenable number.

21831309 is a deficient number, since it is larger than the sum of its proper divisors (10583731).

21831309 is an equidigital number, since it uses as much as digits as its factorization.

21831309 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1817 (or 1811 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 21831309 is about 4672.3986345345. The cubic root of 21831309 is about 279.4859147005.

The spelling of 21831309 in words is "twenty-one million, eight hundred thirty-one thousand, three hundred nine".