79905721 has 9 divisors (see below), whose sum is σ = 93024399. Its totient is φ = 68436984.

The previous prime is 79905691. The next prime is 79905731. The reversal of 79905721 is 12750997.

The square root of 79905721 is 8939.

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

It can be written as a sum of positive squares in only one way, i.e., 52490025 + 27415696 = 7245^2 + 5236^2 .

It is not a de Polignac number, because 79905721 - 2⁵ = 79905689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (79905731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 61935 + ... + 63211.

Almost surely, 2^79905721 is an apocalyptic number.

79905721 is the 8939-th square number.

79905721 is the 4470-th centered octagonal number.

It is an amenable number.

79905721 is a deficient number, since it is larger than the sum of its proper divisors (13118678).

79905721 is an frugal number, since it uses more digits than its factorization.

79905721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2568 (or 1284 counting only the distinct ones).

The product of its (nonzero) digits is 39690, while the sum is 40.

The cubic root of 79905721 is about 430.7176065138.

The spelling of 79905721 in words is "seventy-nine million, nine hundred five thousand, seven hundred twenty-one".