15816388921 has 2 divisors, whose sum is σ = 15816388922. Its totient is φ = 15816388920.

The previous prime is 15816388901. The next prime is 15816388961. The reversal of 15816388921 is 12988361851.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15605006400 + 211382521 = 124920^2 + 14539^2 .

It is a cyclic number.

It is not a de Polignac number, because 15816388921 - 2²⁵ = 15782834489 is a prime.

It is not a weakly prime, because it can be changed into another prime (15816388901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 7908194460 + 7908194461.

It is an arithmetic number, because the mean of its divisors is an integer number (7908194461).

Almost surely, 2^15816388921 is an apocalyptic number.

It is an amenable number.

15816388921 is a deficient number, since it is larger than the sum of its proper divisors (1).

15816388921 is an equidigital number, since it uses as much as digits as its factorization.

15816388921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 829440, while the sum is 52.

The spelling of 15816388921 in words is "fifteen billion, eight hundred sixteen million, three hundred eighty-eight thousand, nine hundred twenty-one".