15921554721 has 8 divisors (see below), whose sum is σ = 21289918944. Its totient is φ = 10583780160.

The previous prime is 15921554713. The next prime is 15921554777. The reversal of 15921554721 is 12745512951.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 15921554721 - 2³ = 15921554713 is a prime.

It is not an unprimeable number, because it can be changed into a prime (15921554021) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7646200 + ... + 7648281.

It is an arithmetic number, because the mean of its divisors is an integer number (2661239868).

Almost surely, 2^15921554721 is an apocalyptic number.

It is an amenable number.

15921554721 is a deficient number, since it is larger than the sum of its proper divisors (5368364223).

15921554721 is a wasteful number, since it uses less digits than its factorization.

15921554721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15294831.

The product of its digits is 126000, while the sum is 42.

The spelling of 15921554721 in words is "fifteen billion, nine hundred twenty-one million, five hundred fifty-four thousand, seven hundred twenty-one".