21309393 has 16 divisors (see below), whose sum is σ = 34181120. Its totient is φ = 11535696.

The previous prime is 21309383. The next prime is 21309397. The reversal of 21309393 is 39390312.

It is not a de Polignac number, because 21309393 - 2¹⁰ = 21308369 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21309393.

It is not an unprimeable number, because it can be changed into a prime (21309397) 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, 26305 + ... + 27102.

It is an arithmetic number, because the mean of its divisors is an integer number (2136320).

Almost surely, 2^21309393 is an apocalyptic number.

It is an amenable number.

21309393 is a deficient number, since it is larger than the sum of its proper divisors (12871727).

21309393 is a wasteful number, since it uses less digits than its factorization.

21309393 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 53436.

The product of its (nonzero) digits is 4374, while the sum is 30.

The square root of 21309393 is about 4616.2098089233. The cubic root of 21309393 is about 277.2407252830.

The spelling of 21309393 in words is "twenty-one million, three hundred nine thousand, three hundred ninety-three".