645718 has 4 divisors (see below), whose sum is σ = 968580. Its totient is φ = 322858.

The previous prime is 645713. The next prime is 645727. The reversal of 645718 is 817546.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 817546 = 2 ⋅408773.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an Ulam number.

It is a self number, because there is not a number n which added to its sum of digits gives 645718.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645713) by changing a digit.

645718 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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 as a sum of consecutive naturals, namely, 161428 + ... + 161431.

It is an arithmetic number, because the mean of its divisors is an integer number (242145).

2⁶⁴⁵⁷¹⁸ is an apocalyptic number.

645718 is a deficient number, since it is larger than the sum of its proper divisors (322862).

645718 is a wasteful number, since it uses less digits than its factorization.

645718 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 322861.

The product of its digits is 6720, while the sum is 31.

The square root of 645718 is about 803.5658031549. The cubic root of 645718 is about 86.4332740781.

The spelling of 645718 in words is "six hundred forty-five thousand, seven hundred eighteen".