15651591721 has 4 divisors (see below), whose sum is σ = 15709346944. Its totient is φ = 15593836500.

The previous prime is 15651591713. The next prime is 15651591743. The reversal of 15651591721 is 12719515651.

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, and also an emirpimes, since its reverse is a distinct semiprime: 12719515651 = 17 ⋅748206803.

It is a cyclic number.

It is not a de Polignac number, because 15651591721 - 2³ = 15651591713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (15651591821) 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, 28877205 + ... + 28877746.

It is an arithmetic number, because the mean of its divisors is an integer number (3927336736).

Almost surely, 2^15651591721 is an apocalyptic number.

It is an amenable number.

15651591721 is a deficient number, since it is larger than the sum of its proper divisors (57755223).

15651591721 is an equidigital number, since it uses as much as digits as its factorization.

15651591721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57755222.

The product of its digits is 94500, while the sum is 43.

The spelling of 15651591721 in words is "fifteen billion, six hundred fifty-one million, five hundred ninety-one thousand, seven hundred twenty-one".