815730721 has 9 divisors (see below), whose sum is σ = 883708281. Its totient is φ = 752982204.

The previous prime is 815730701. The next prime is 815730739. The reversal of 815730721 is 127037518.

The square root of 815730721 is 28561.

It is a perfect power (a square, a biquadrate, a 8-th power), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 57121 + 815673600 = 239^2 + 28560^2 .

It is not a de Polignac number, because 815730721 - 2¹¹ = 815728673 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 13.

It is not an unprimeable number, because it can be changed into a prime (815730701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 62748511 + ... + 62748523.

It is an arithmetic number, because the mean of its divisors is an integer number (98189809).

Almost surely, 2^815730721 is an apocalyptic number.

815730721 is the 28561-st square number.

815730721 is the 14281-st centered octagonal number.

It is an amenable number.

815730721 is a deficient number, since it is larger than the sum of its proper divisors (67977560).

815730721 is an frugal number, since it uses more digits than its factorization.

815730721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 104 (or 13 counting only the distinct ones).

The product of its (nonzero) digits is 11760, while the sum is 34.

The cubic root of 815730721 is about 934.3629435117.

The spelling of 815730721 in words is "eight hundred fifteen million, seven hundred thirty thousand, seven hundred twenty-one".