16991521387 has 4 divisors (see below), whose sum is σ = 17046156816. Its totient is φ = 16936885960.

The previous prime is 16991521373. The next prime is 16991521441. The reversal of 16991521387 is 78312519961.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 78312519961 = 13 ⋅6024039997.

It is a cyclic number.

It is not a de Polignac number, because 16991521387 - 2²³ = 16983132779 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16991521367) 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, 27317248 + ... + 27317869.

It is an arithmetic number, because the mean of its divisors is an integer number (4261539204).

Almost surely, 2^16991521387 is an apocalyptic number.

16991521387 is a deficient number, since it is larger than the sum of its proper divisors (54635429).

16991521387 is an equidigital number, since it uses as much as digits as its factorization.

16991521387 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 54635428.

The product of its digits is 816480, while the sum is 52.

The spelling of 16991521387 in words is "sixteen billion, nine hundred ninety-one million, five hundred twenty-one thousand, three hundred eighty-seven".