521721 has 24 divisors (see below), whose sum is σ = 829920. Its totient is φ = 326592.

The previous prime is 521707. The next prime is 521723. The reversal of 521721 is 127125.

521721 is nontrivially palindromic in base 8.

It is not a de Polignac number, because 521721 - 2⁶ = 521657 is a prime.

It is a hoax number, since the sum of its digits (18) coincides with the sum of the digits of its distinct prime factors.

It is a junction number, because it is equal to n+sod(n) for n = 521694 and 521703.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 521721.

It is not an unprimeable number, because it can be changed into a prime (521723) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4561 + ... + 4673.

It is an arithmetic number, because the mean of its divisors is an integer number (34580).

2⁵²¹⁷²¹ is an apocalyptic number.

It is an amenable number.

521721 is a deficient number, since it is larger than the sum of its proper divisors (308199).

521721 is a wasteful number, since it uses less digits than its factorization.

521721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 147 (or 135 counting only the distinct ones).

The product of its digits is 140, while the sum is 18.

The square root of 521721 is about 722.3025681804. The cubic root of 521721 is about 80.5031311874.

Adding to 521721 its reverse (127125), we get a palindrome (648846).

The spelling of 521721 in words is "five hundred twenty-one thousand, seven hundred twenty-one".