15691679921 has 4 divisors (see below), whose sum is σ = 15844026432. Its totient is φ = 15539333412.

The previous prime is 15691679911. The next prime is 15691679933. The reversal of 15691679921 is 12997619651.

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: 12997619651 = 62549 ⋅207799.

It is a cyclic number.

It is not a de Polignac number, because 15691679921 - 2²² = 15687485617 is a prime.

It is a super-2 number, since 2×15691679921² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (15691679911) 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, 76173101 + ... + 76173306.

It is an arithmetic number, because the mean of its divisors is an integer number (3961006608).

Almost surely, 2^15691679921 is an apocalyptic number.

It is an amenable number.

15691679921 is a deficient number, since it is larger than the sum of its proper divisors (152346511).

15691679921 is a wasteful number, since it uses less digits than its factorization.

15691679921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 152346510.

The product of its digits is 1837080, while the sum is 56.

The spelling of 15691679921 in words is "fifteen billion, six hundred ninety-one million, six hundred seventy-nine thousand, nine hundred twenty-one".