664221 has 16 divisors (see below), whose sum is σ = 957440. Its totient is φ = 408240.

The previous prime is 664211. The next prime is 664243. The reversal of 664221 is 122466.

It is a happy number.

It is not a de Polignac number, because 664221 - 2⁹ = 663709 is a prime.

It is a Duffinian number.

664221 is a lucky number.

It is a nialpdrome in base 10.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (664211) 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, 2316 + ... + 2586.

It is an arithmetic number, because the mean of its divisors is an integer number (59840).

2⁶⁶⁴²²¹ is an apocalyptic number.

It is an amenable number.

664221 is a deficient number, since it is larger than the sum of its proper divisors (293219).

664221 is a wasteful number, since it uses less digits than its factorization.

664221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 336.

The product of its digits is 576, while the sum is 21.

The square root of 664221 is about 814.9975460086. The cubic root of 664221 is about 87.2510912472.

Adding to 664221 its reverse (122466), we get a palindrome (786687).

The spelling of 664221 in words is "six hundred sixty-four thousand, two hundred twenty-one".