6666521 has 4 divisors (see below), whose sum is σ = 6681444. Its totient is φ = 6651600.

The previous prime is 6666509. The next prime is 6666523. The reversal of 6666521 is 1256666.

6666521 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.

It can be written as a sum of positive squares in 2 ways, for example, as 1073296 + 5593225 = 1036^2 + 2365^2 .

It is a cyclic number.

It is not a de Polignac number, because 6666521 - 2¹⁰ = 6665497 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 10.

It is not an unprimeable number, because it can be changed into a prime (6666523) 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, 6770 + ... + 7691.

It is an arithmetic number, because the mean of its divisors is an integer number (1670361).

Almost surely, 2^6666521 is an apocalyptic number.

It is an amenable number.

6666521 is a deficient number, since it is larger than the sum of its proper divisors (14923).

6666521 is a wasteful number, since it uses less digits than its factorization.

6666521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14922.

The product of its digits is 12960, while the sum is 32.

The square root of 6666521 is about 2581.9606890888. The cubic root of 6666521 is about 188.2058349904.

The spelling of 6666521 in words is "six million, six hundred sixty-six thousand, five hundred twenty-one".