521135721 has 8 divisors (see below), whose sum is σ = 772052960. Its totient is φ = 347423796.

The previous prime is 521135711. The next prime is 521135759. The reversal of 521135721 is 127531125.

521135721 is a `hidden beast` number, since 521 + 135 + 7 + 2 + 1 = 666.

It is not a de Polignac number, because 521135721 - 2¹⁴ = 521119337 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 19301323 = 521135721 / (5 + 2 + 1 + 1 + 3 + 5 + 7 + 2 + 1).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (521135711) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9650635 + ... + 9650688.

It is an arithmetic number, because the mean of its divisors is an integer number (96506620).

Almost surely, 2^521135721 is an apocalyptic number.

It is an amenable number.

521135721 is a deficient number, since it is larger than the sum of its proper divisors (250917239).

521135721 is a wasteful number, since it uses less digits than its factorization.

521135721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19301332 (or 19301326 counting only the distinct ones).

The product of its digits is 2100, while the sum is 27.

The square root of 521135721 is about 22828.3972499166. The cubic root of 521135721 is about 804.7301648244.

Adding to 521135721 its reverse (127531125), we get a palindrome (648666846).

The spelling of 521135721 in words is "five hundred twenty-one million, one hundred thirty-five thousand, seven hundred twenty-one".