21958115921 has 4 divisors (see below), whose sum is σ = 25094989632. Its totient is φ = 18821242212.

The previous prime is 21958115903. The next prime is 21958115929. The reversal of 21958115921 is 12951185912.

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 21958115921 - 2¹⁸ = 21957853777 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21958115929) 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, 1568436845 + ... + 1568436858.

It is an arithmetic number, because the mean of its divisors is an integer number (6273747408).

Almost surely, 2^21958115921 is an apocalyptic number.

It is an amenable number.

21958115921 is a deficient number, since it is larger than the sum of its proper divisors (3136873711).

21958115921 is an equidigital number, since it uses as much as digits as its factorization.

21958115921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3136873710.

The product of its digits is 64800, while the sum is 44.

The spelling of 21958115921 in words is "twenty-one billion, nine hundred fifty-eight million, one hundred fifteen thousand, nine hundred twenty-one".