21123189209 has 4 divisors (see below), whose sum is σ = 21132100560. Its totient is φ = 21114277860.

The previous prime is 21123189137. The next prime is 21123189271. The reversal of 21123189209 is 90298132112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21123189209 - 2¹² = 21123185113 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21123189509) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4452119 + ... + 4456860.

It is an arithmetic number, because the mean of its divisors is an integer number (5283025140).

Almost surely, 2^21123189209 is an apocalyptic number.

It is an amenable number.

21123189209 is a deficient number, since it is larger than the sum of its proper divisors (8911351).

21123189209 is an equidigital number, since it uses as much as digits as its factorization.

21123189209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8911350.

The product of its (nonzero) digits is 15552, while the sum is 38.

The spelling of 21123189209 in words is "twenty-one billion, one hundred twenty-three million, one hundred eighty-nine thousand, two hundred nine".