16521099991 has 4 divisors (see below), whose sum is σ = 18023018184. Its totient is φ = 15019181800.

The previous prime is 16521099989. The next prime is 16521100009. The reversal of 16521099991 is 19999012561.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 16521099991 - 2¹ = 16521099989 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16521099941) 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, 750959080 + ... + 750959101.

It is an arithmetic number, because the mean of its divisors is an integer number (4505754546).

Almost surely, 2^16521099991 is an apocalyptic number.

16521099991 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

16521099991 is a deficient number, since it is larger than the sum of its proper divisors (1501918193).

16521099991 is a wasteful number, since it uses less digits than its factorization.

16521099991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1501918192.

The product of its (nonzero) digits is 393660, while the sum is 52.

The spelling of 16521099991 in words is "sixteen billion, five hundred twenty-one million, ninety-nine thousand, nine hundred ninety-one".