681563521 has 4 divisors (see below), whose sum is σ = 681737044. Its totient is φ = 681390000.

The previous prime is 681563479. The next prime is 681563527. The reversal of 681563521 is 125365186.

681563521 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It can be written as a sum of positive squares in 2 ways, for example, as 301508496 + 380055025 = 17364^2 + 19495^2 .

It is a cyclic number.

It is not a de Polignac number, because 681563521 - 2¹⁷ = 681432449 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (681563527) 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, 80730 + ... + 88771.

It is an arithmetic number, because the mean of its divisors is an integer number (170434261).

Almost surely, 2^681563521 is an apocalyptic number.

It is an amenable number.

681563521 is a deficient number, since it is larger than the sum of its proper divisors (173523).

681563521 is a wasteful number, since it uses less digits than its factorization.

681563521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 173522.

The product of its digits is 43200, while the sum is 37.

The square root of 681563521 is about 26106.7715545220. The cubic root of 681563521 is about 880.0393926064.

The spelling of 681563521 in words is "six hundred eighty-one million, five hundred sixty-three thousand, five hundred twenty-one".