521681 has 4 divisors (see below), whose sum is σ = 539700. Its totient is φ = 503664.

The previous prime is 521671. The next prime is 521693. The reversal of 521681 is 186125.

521681 is nontrivially palindromic in base 14.

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 341056 + 180625 = 584^2 + 425^2 .

It is a cyclic number.

It is not a de Polignac number, because 521681 - 2¹⁸ = 259537 is a prime.

It is a super-2 number, since 2×521681² = 544302131522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (521641) 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 3 ways as a sum of consecutive naturals, for example, 8966 + ... + 9023.

It is an arithmetic number, because the mean of its divisors is an integer number (134925).

2⁵²¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

521681 is a deficient number, since it is larger than the sum of its proper divisors (18019).

521681 is a wasteful number, since it uses less digits than its factorization.

521681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18018.

The product of its digits is 480, while the sum is 23.

The square root of 521681 is about 722.2748784223. The cubic root of 521681 is about 80.5010737611.

The spelling of 521681 in words is "five hundred twenty-one thousand, six hundred eighty-one".