8720021 has 4 divisors (see below), whose sum is σ = 9001344. Its totient is φ = 8438700.

The previous prime is 8719999. The next prime is 8720027. The reversal of 8720021 is 1200278.

8720021 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

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-8720021 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 8719975 and 8720002.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (8720027) 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, 140615 + ... + 140676.

It is an arithmetic number, because the mean of its divisors is an integer number (2250336).

Almost surely, 2^8720021 is an apocalyptic number.

It is an amenable number.

8720021 is a deficient number, since it is larger than the sum of its proper divisors (281323).

8720021 is a wasteful number, since it uses less digits than its factorization.

8720021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 281322.

The product of its (nonzero) digits is 224, while the sum is 20.

The square root of 8720021 is about 2952.9681677932. The cubic root of 8720021 is about 205.8286585435.

Adding to 8720021 its reverse (1200278), we get a palindrome (9920299).

The spelling of 8720021 in words is "eight million, seven hundred twenty thousand, twenty-one".