521801991 has 12 divisors (see below), whose sum is σ = 766070760. Its totient is φ = 342164880.

The previous prime is 521801981. The next prime is 521801999. The reversal of 521801991 is 199108125.

It is not a de Polignac number, because 521801991 - 2¹⁵ = 521769223 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (521801999) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 474681 + ... + 475778.

It is an arithmetic number, because the mean of its divisors is an integer number (63839230).

Almost surely, 2^521801991 is an apocalyptic number.

521801991 is a deficient number, since it is larger than the sum of its proper divisors (244268769).

521801991 is a wasteful number, since it uses less digits than its factorization.

521801991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 950526 (or 950523 counting only the distinct ones).

The product of its (nonzero) digits is 6480, while the sum is 36.

The square root of 521801991 is about 22842.9855973338. The cubic root of 521801991 is about 805.0729669080.

The spelling of 521801991 in words is "five hundred twenty-one million, eight hundred one thousand, nine hundred ninety-one".