82720721 has 4 divisors (see below), whose sum is σ = 82747392. Its totient is φ = 82694052.

The previous prime is 82720709. The next prime is 82720747. The reversal of 82720721 is 12702728.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-82720721 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (82720321) 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, 7961 + ... + 15126.

It is an arithmetic number, because the mean of its divisors is an integer number (20686848).

Almost surely, 2^82720721 is an apocalyptic number.

It is an amenable number.

82720721 is a deficient number, since it is larger than the sum of its proper divisors (26671).

82720721 is a wasteful number, since it uses less digits than its factorization.

82720721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26670.

The product of its (nonzero) digits is 3136, while the sum is 29.

The square root of 82720721 is about 9095.0932375650. The cubic root of 82720721 is about 435.7172664748.

The spelling of 82720721 in words is "eighty-two million, seven hundred twenty thousand, seven hundred twenty-one".