666920221 has 16 divisors (see below), whose sum is σ = 753805440. Its totient is φ = 584476480.

The previous prime is 666920161. The next prime is 666920231. The reversal of 666920221 is 122029666.

It is a cyclic number.

It is not a de Polignac number, because 666920221 - 2¹¹ = 666918173 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666920231) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 281775 + ... + 284131.

It is an arithmetic number, because the mean of its divisors is an integer number (47112840).

Almost surely, 2^666920221 is an apocalyptic number.

It is an amenable number.

666920221 is a deficient number, since it is larger than the sum of its proper divisors (86885219).

666920221 is a wasteful number, since it uses less digits than its factorization.

666920221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3284.

The product of its (nonzero) digits is 15552, while the sum is 34.

The square root of 666920221 is about 25824.7985664942. The cubic root of 666920221 is about 873.6912007549.

Adding to 666920221 its reverse (122029666), we get a palindrome (788949887).

The spelling of 666920221 in words is "six hundred sixty-six million, nine hundred twenty thousand, two hundred twenty-one".