666655221 has 8 divisors (see below), whose sum is σ = 941160384. Its totient is φ = 418293440.

The previous prime is 666655211. The next prime is 666655267. The reversal of 666655221 is 122556666.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 666655221 - 2¹⁴ = 666638837 is a prime.

It is a Curzon number.

It is a nialpdrome in base 10.

It is a self number, because there is not a number n which added to its sum of digits gives 666655221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666655211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6535785 + ... + 6535886.

It is an arithmetic number, because the mean of its divisors is an integer number (117645048).

Almost surely, 2^666655221 is an apocalyptic number.

It is an amenable number.

666655221 is a deficient number, since it is larger than the sum of its proper divisors (274505163).

666655221 is a wasteful number, since it uses less digits than its factorization.

666655221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13071691.

The product of its digits is 129600, while the sum is 39.

The square root of 666655221 is about 25819.6673293828. The cubic root of 666655221 is about 873.5754653523.

The spelling of 666655221 in words is "six hundred sixty-six million, six hundred fifty-five thousand, two hundred twenty-one".