664681 has 4 divisors (see below), whose sum is σ = 671364. Its totient is φ = 658000.

The previous prime is 664679. The next prime is 664687. The reversal of 664681 is 186466.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 434281 + 230400 = 659^2 + 480^2 .

It is a cyclic number.

It is not a de Polignac number, because 664681 - 2¹ = 664679 is a prime.

It is a super-4 number, since 4×664681⁴ (a number of 24 digits) contains 4444 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (664687) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3190 + ... + 3391.

It is an arithmetic number, because the mean of its divisors is an integer number (167841).

2⁶⁶⁴⁶⁸¹ is an apocalyptic number.

It is an amenable number.

664681 is a deficient number, since it is larger than the sum of its proper divisors (6683).

664681 is a wasteful number, since it uses less digits than its factorization.

664681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6682.

The product of its digits is 6912, while the sum is 31.

The square root of 664681 is about 815.2797066038. The cubic root of 664681 is about 87.2712282400.

The spelling of 664681 in words is "six hundred sixty-four thousand, six hundred eighty-one".