6557721 has 4 divisors (see below), whose sum is σ = 8743632. Its totient is φ = 4371812.

The previous prime is 6557693. The next prime is 6557723. The reversal of 6557721 is 1277556.

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 6557721 - 2⁵ = 6557689 is a prime.

It is a D-number.

It is not an unprimeable number, because it can be changed into a prime (6557723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1092951 + ... + 1092956.

It is an arithmetic number, because the mean of its divisors is an integer number (2185908).

Almost surely, 2^6557721 is an apocalyptic number.

It is an amenable number.

6557721 is a deficient number, since it is larger than the sum of its proper divisors (2185911).

6557721 is a wasteful number, since it uses less digits than its factorization.

6557721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2185910.

The product of its digits is 14700, while the sum is 33.

The square root of 6557721 is about 2560.8047563217. The cubic root of 6557721 is about 187.1763518871.

The spelling of 6557721 in words is "six million, five hundred fifty-seven thousand, seven hundred twenty-one".