21210809123 has 4 divisors (see below), whose sum is σ = 24240924720. Its totient is φ = 18180693528.

The previous prime is 21210809083. The next prime is 21210809141. The reversal of 21210809123 is 32190801212.

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 21210809123 - 2¹⁸ = 21210546979 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21210809143) 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, 1515057788 + ... + 1515057801.

It is an arithmetic number, because the mean of its divisors is an integer number (6060231180).

Almost surely, 2^21210809123 is an apocalyptic number.

21210809123 is a deficient number, since it is larger than the sum of its proper divisors (3030115597).

21210809123 is an equidigital number, since it uses as much as digits as its factorization.

21210809123 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3030115596.

The product of its (nonzero) digits is 1728, while the sum is 29.

The spelling of 21210809123 in words is "twenty-one billion, two hundred ten million, eight hundred nine thousand, one hundred twenty-three".