8720721 has 12 divisors (see below), whose sum is σ = 12689040. Its totient is φ = 5771160.

The previous prime is 8720713. The next prime is 8720729. The reversal of 8720721 is 1270278.

It is an interprime number because it is at equal distance from previous prime (8720713) and next prime (8720729).

It is not a de Polignac number, because 8720721 - 2³ = 8720713 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (8720729) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2235 + ... + 4736.

It is an arithmetic number, because the mean of its divisors is an integer number (1057420).

Almost surely, 2^8720721 is an apocalyptic number.

It is an amenable number.

8720721 is a deficient number, since it is larger than the sum of its proper divisors (3968319).

8720721 is a wasteful number, since it uses less digits than its factorization.

8720721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7116 (or 7113 counting only the distinct ones).

The product of its (nonzero) digits is 1568, while the sum is 27.

The square root of 8720721 is about 2953.0866902277. The cubic root of 8720721 is about 205.8341660304.

Adding to 8720721 its reverse (1270278), we get a palindrome (9990999).

The spelling of 8720721 in words is "eight million, seven hundred twenty thousand, seven hundred twenty-one".