21308851 has 4 divisors (see below), whose sum is σ = 21330400. Its totient is φ = 21287304.

The previous prime is 21308831. The next prime is 21308867. The reversal of 21308851 is 15880312.

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 21308851 - 2⁷ = 21308723 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21308801) 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, 9216 + ... + 11293.

It is an arithmetic number, because the mean of its divisors is an integer number (5332600).

Almost surely, 2^21308851 is an apocalyptic number.

21308851 is a deficient number, since it is larger than the sum of its proper divisors (21549).

21308851 is a wasteful number, since it uses less digits than its factorization.

21308851 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21548.

The product of its (nonzero) digits is 1920, while the sum is 28.

The square root of 21308851 is about 4616.1511023796. The cubic root of 21308851 is about 277.2383747429.

The spelling of 21308851 in words is "twenty-one million, three hundred eight thousand, eight hundred fifty-one".