664691 has 2 divisors, whose sum is σ = 664692. Its totient is φ = 664690.

The previous prime is 664687. The next prime is 664693. The reversal of 664691 is 196466.

664691 is nontrivially palindromic in base 5.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 664691 - 2² = 664687 is a prime.

Together with 664693, it forms a pair of twin primes.

It is a Chen prime.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 664691.

It is not a weakly prime, because it can be changed into another prime (664693) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332345 + 332346.

It is an arithmetic number, because the mean of its divisors is an integer number (332346).

2⁶⁶⁴⁶⁹¹ is an apocalyptic number.

664691 is a deficient number, since it is larger than the sum of its proper divisors (1).

664691 is an equidigital number, since it uses as much as digits as its factorization.

664691 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7776, while the sum is 32.

The square root of 664691 is about 815.2858394453. The cubic root of 664691 is about 87.2716658975.

The spelling of 664691 in words is "six hundred sixty-four thousand, six hundred ninety-one".