664391731 has 6 divisors (see below), whose sum is σ = 694534820. Its totient is φ = 635504628.

The previous prime is 664391723. The next prime is 664391771. The reversal of 664391731 is 137193466.

664391731 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 664391731 - 2³ = 664391723 is a prime.

It is a super-2 number, since 2×664391731² = 882832744442352722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (664391771) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 627441 + ... + 628498.

Almost surely, 2^664391731 is an apocalyptic number.

664391731 is a deficient number, since it is larger than the sum of its proper divisors (30143089).

664391731 is a wasteful number, since it uses less digits than its factorization.

664391731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1255985 (or 1255962 counting only the distinct ones).

The product of its digits is 81648, while the sum is 40.

The square root of 664391731 is about 25775.7973882478. The cubic root of 664391731 is about 872.5856626429.

The spelling of 664391731 in words is "six hundred sixty-four million, three hundred ninety-one thousand, seven hundred thirty-one".