645731 has 4 divisors (see below), whose sum is σ = 660792. Its totient is φ = 630672.

The previous prime is 645727. The next prime is 645737. The reversal of 645731 is 137546.

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

It is a cyclic number.

It is not a de Polignac number, because 645731 - 2² = 645727 is a prime.

It is a super-2 number, since 2×645731² = 833937048722, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 645731.

It is not an unprimeable number, because it can be changed into a prime (645737) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7466 + ... + 7551.

It is an arithmetic number, because the mean of its divisors is an integer number (165198).

2⁶⁴⁵⁷³¹ is an apocalyptic number.

645731 is a deficient number, since it is larger than the sum of its proper divisors (15061).

645731 is a wasteful number, since it uses less digits than its factorization.

645731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15060.

The product of its digits is 2520, while the sum is 26.

The square root of 645731 is about 803.5738920597. The cubic root of 645731 is about 86.4338541172.

The spelling of 645731 in words is "six hundred forty-five thousand, seven hundred thirty-one".