521253721 has 4 divisors (see below), whose sum is σ = 521889444. Its totient is φ = 520618000.

The previous prime is 521253713. The next prime is 521253749. The reversal of 521253721 is 127352125.

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 118810000 + 402443721 = 10900^2 + 20061^2 .

It is a cyclic number.

It is not a de Polignac number, because 521253721 - 2³ = 521253713 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 521253721.

It is not an unprimeable number, because it can be changed into a prime (521253751) 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, 316630 + ... + 318271.

It is an arithmetic number, because the mean of its divisors is an integer number (130472361).

Almost surely, 2^521253721 is an apocalyptic number.

It is an amenable number.

521253721 is a deficient number, since it is larger than the sum of its proper divisors (635723).

521253721 is an equidigital number, since it uses as much as digits as its factorization.

521253721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 635722.

The product of its digits is 4200, while the sum is 28.

The square root of 521253721 is about 22830.9816039521. The cubic root of 521253721 is about 804.7908981993.

The spelling of 521253721 in words is "five hundred twenty-one million, two hundred fifty-three thousand, seven hundred twenty-one".