664421 has 2 divisors, whose sum is σ = 664422. Its totient is φ = 664420.

The previous prime is 664403. The next prime is 664427. The reversal of 664421 is 124466.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 664225 + 196 = 815^2 + 14^2 .

It is a cyclic number.

It is not a de Polignac number, because 664421 - 2⁶ = 664357 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a nialpdrome in base 10.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (664427) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332210 + 332211.

It is an arithmetic number, because the mean of its divisors is an integer number (332211).

2⁶⁶⁴⁴²¹ is an apocalyptic number.

It is an amenable number.

664421 is a deficient number, since it is larger than the sum of its proper divisors (1).

664421 is an equidigital number, since it uses as much as digits as its factorization.

664421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1152, while the sum is 23.

The square root of 664421 is about 815.1202365296. The cubic root of 664421 is about 87.2598476035.

Adding to 664421 its reverse (124466), we get a palindrome (788887).

The spelling of 664421 in words is "six hundred sixty-four thousand, four hundred twenty-one".