21121311209 has 4 divisors (see below), whose sum is σ = 21129465600. Its totient is φ = 21113156820.

The previous prime is 21121311191. The next prime is 21121311307. The reversal of 21121311209 is 90211312112.

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 21121311209 - 2²⁸ = 20852875753 is a prime.

It is a super-2 number, since 2×21121311209² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21121311109) 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, 4073309 + ... + 4078490.

It is an arithmetic number, because the mean of its divisors is an integer number (5282366400).

Almost surely, 2^21121311209 is an apocalyptic number.

It is an amenable number.

21121311209 is a deficient number, since it is larger than the sum of its proper divisors (8154391).

21121311209 is an equidigital number, since it uses as much as digits as its factorization.

21121311209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8154390.

The product of its (nonzero) digits is 216, while the sum is 23.

The spelling of 21121311209 in words is "twenty-one billion, one hundred twenty-one million, three hundred eleven thousand, two hundred nine".