8556721 has 4 divisors (see below), whose sum is σ = 8572912. Its totient is φ = 8540532.

The previous prime is 8556697. The next prime is 8556739. The reversal of 8556721 is 1276558.

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 not a de Polignac number, because 8556721 - 2²¹ = 6459569 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (8556761) 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, 7275 + ... + 8368.

It is an arithmetic number, because the mean of its divisors is an integer number (2143228).

Almost surely, 2^8556721 is an apocalyptic number.

It is an amenable number.

8556721 is a deficient number, since it is larger than the sum of its proper divisors (16191).

8556721 is a wasteful number, since it uses less digits than its factorization.

8556721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16190.

The product of its digits is 16800, while the sum is 34.

The square root of 8556721 is about 2925.1873444277. The cubic root of 8556721 is about 204.5357011496.

The spelling of 8556721 in words is "eight million, five hundred fifty-six thousand, seven hundred twenty-one".