79721581 has 4 divisors (see below), whose sum is σ = 79756732. Its totient is φ = 79686432.

The previous prime is 79721573. The next prime is 79721591. The reversal of 79721581 is 18512797.

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 61308900 + 18412681 = 7830^2 + 4291^2 .

It is a cyclic number.

It is not a de Polignac number, because 79721581 - 2³ = 79721573 is a prime.

It is a super-2 number, since 2×79721581² = 12711060954279122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (79721501) 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, 13920 + ... + 18793.

It is an arithmetic number, because the mean of its divisors is an integer number (19939183).

Almost surely, 2^79721581 is an apocalyptic number.

It is an amenable number.

79721581 is a deficient number, since it is larger than the sum of its proper divisors (35151).

79721581 is a wasteful number, since it uses less digits than its factorization.

79721581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35150.

The product of its digits is 35280, while the sum is 40.

The square root of 79721581 is about 8928.6942494410. The cubic root of 79721581 is about 430.3864940420.

The spelling of 79721581 in words is "seventy-nine million, seven hundred twenty-one thousand, five hundred eighty-one".