21308911 has 4 divisors (see below), whose sum is σ = 22948072. Its totient is φ = 19669752.

The previous prime is 21308897. The next prime is 21308921. The reversal of 21308911 is 11980312.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21308911 - 2¹⁹ = 20784623 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 (21308921) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 819561 + ... + 819586.

It is an arithmetic number, because the mean of its divisors is an integer number (5737018).

Almost surely, 2^21308911 is an apocalyptic number.

21308911 is a deficient number, since it is larger than the sum of its proper divisors (1639161).

21308911 is a wasteful number, since it uses less digits than its factorization.

21308911 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1639160.

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

The square root of 21308911 is about 4616.1576012957. The cubic root of 21308911 is about 277.2386349522.

The spelling of 21308911 in words is "twenty-one million, three hundred eight thousand, nine hundred eleven".