815923921921 has 4 divisors (see below), whose sum is σ = 851398875072. Its totient is φ = 780448968772.

The previous prime is 815923921867. The next prime is 815923921931. The reversal of 815923921921 is 129129329518.

It is a happy number.

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 815923921921 - 2²³ = 815915533313 is a prime.

It is a super-2 number, since 2×815923921921² (a number of 25 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (815923921931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17737476541 + ... + 17737476586.

It is an arithmetic number, because the mean of its divisors is an integer number (212849718768).

Almost surely, 2^815923921921 is an apocalyptic number.

It is an amenable number.

815923921921 is a deficient number, since it is larger than the sum of its proper divisors (35474953151).

815923921921 is a wasteful number, since it uses less digits than its factorization.

815923921921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35474953150.

The product of its digits is 699840, while the sum is 52.

The spelling of 815923921921 in words is "eight hundred fifteen billion, nine hundred twenty-three million, nine hundred twenty-one thousand, nine hundred twenty-one".