666044021 has 4 divisors (see below), whose sum is σ = 687529344. Its totient is φ = 644558700.

The previous prime is 666044009. The next prime is 666044033. The reversal of 666044021 is 120440666.

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 an interprime number because it is at equal distance from previous prime (666044009) and next prime (666044033).

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-666044021 is a prime.

It is a super-2 number, since 2×666044021² = 887229275819696882, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666047021) 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, 10742615 + ... + 10742676.

It is an arithmetic number, because the mean of its divisors is an integer number (171882336).

Almost surely, 2^666044021 is an apocalyptic number.

It is an amenable number.

666044021 is a deficient number, since it is larger than the sum of its proper divisors (21485323).

666044021 is a wasteful number, since it uses less digits than its factorization.

666044021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21485322.

The product of its (nonzero) digits is 6912, while the sum is 29.

The square root of 666044021 is about 25807.8286765857. The cubic root of 666044021 is about 873.3084144778.

Adding to 666044021 its reverse (120440666), we get a palindrome (786484687).

The spelling of 666044021 in words is "six hundred sixty-six million, forty-four thousand, twenty-one".