531809721 has 9 divisors (see below), whose sum is σ = 768269541. Its totient is φ = 354493692.

The previous prime is 531809701. The next prime is 531809723. The reversal of 531809721 is 127908135.

The square root of 531809721 is 23061.

It is a perfect power (a square), and thus also a powerful number.

It is a tau number, because it is divible by the number of its divisors (9).

It is not a de Polignac number, because 531809721 - 2²¹ = 529712569 is a prime.

It is not an unprimeable number, because it can be changed into a prime (531809723) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 65340 + ... + 73026.

Almost surely, 2^531809721 is an apocalyptic number.

531809721 is the 23061-st square number.

531809721 is the 11531-st centered octagonal number.

It is an amenable number.

531809721 is a deficient number, since it is larger than the sum of its proper divisors (236459820).

531809721 is an frugal number, since it uses more digits than its factorization.

531809721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15380 (or 7690 counting only the distinct ones).

The product of its (nonzero) digits is 15120, while the sum is 36.

The cubic root of 531809721 is about 810.1872863681.

Multiplying 531809721 by its sum of digits (36), we get a square (19145149956 = 138366²).

The spelling of 531809721 in words is "five hundred thirty-one million, eight hundred nine thousand, seven hundred twenty-one".