991521521 has 4 divisors (see below), whose sum is σ = 995180544. Its totient is φ = 987862500.

The previous prime is 991521493. The next prime is 991521527. The reversal of 991521521 is 125125199.

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.

It is a cyclic number.

It is not a de Polignac number, because 991521521 - 2⁶ = 991521457 is a prime.

It is a super-3 number, since 3×991521521³ (a number of 28 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991521527) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1829105 + ... + 1829646.

It is an arithmetic number, because the mean of its divisors is an integer number (248795136).

Almost surely, 2^991521521 is an apocalyptic number.

It is an amenable number.

991521521 is a deficient number, since it is larger than the sum of its proper divisors (3659023).

991521521 is a wasteful number, since it uses less digits than its factorization.

991521521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3659022.

The product of its digits is 8100, while the sum is 35.

The square root of 991521521 is about 31488.4347181628. The cubic root of 991521521 is about 997.1658153192.

The spelling of 991521521 in words is "nine hundred ninety-one million, five hundred twenty-one thousand, five hundred twenty-one".