664891 has 2 divisors, whose sum is σ = 664892. Its totient is φ = 664890.

The previous prime is 664879. The next prime is 664933. The reversal of 664891 is 198466.

664891 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 664891 - 2⁹ = 664379 is a prime.

It is not a weakly prime, because it can be changed into another prime (664091) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332445 + 332446.

It is an arithmetic number, because the mean of its divisors is an integer number (332446).

2⁶⁶⁴⁸⁹¹ is an apocalyptic number.

664891 is a deficient number, since it is larger than the sum of its proper divisors (1).

664891 is an equidigital number, since it uses as much as digits as its factorization.

664891 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10368, while the sum is 34.

The square root of 664891 is about 815.4084865882. The cubic root of 664891 is about 87.2804181262.

It can be divided in two parts, 66 and 4891, that multiplied together give a triangular number (322806 = T₈₀₃).

The spelling of 664891 in words is "six hundred sixty-four thousand, eight hundred ninety-one".