21000121999 has 4 divisors (see below), whose sum is σ = 21000442320. Its totient is φ = 20999801680.

The previous prime is 21000121997. The next prime is 21000122027. The reversal of 21000121999 is 99912100012.

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 21000121999 - 2¹ = 21000121997 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 (21000121997) 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, 22219 + ... + 206140.

It is an arithmetic number, because the mean of its divisors is an integer number (5250110580).

Almost surely, 2^21000121999 is an apocalyptic number.

21000121999 is a deficient number, since it is larger than the sum of its proper divisors (320321).

21000121999 is an equidigital number, since it uses as much as digits as its factorization.

21000121999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 320320.

The product of its (nonzero) digits is 2916, while the sum is 34.

The spelling of 21000121999 in words is "twenty-one billion, one hundred twenty-one thousand, nine hundred ninety-nine".