645779 has 4 divisors (see below), whose sum is σ = 683784. Its totient is φ = 607776.

The previous prime is 645763. The next prime is 645787. The reversal of 645779 is 977546.

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 645779 - 2⁴ = 645763 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (645739) 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, 18977 + ... + 19010.

It is an arithmetic number, because the mean of its divisors is an integer number (170946).

2⁶⁴⁵⁷⁷⁹ is an apocalyptic number.

645779 is a deficient number, since it is larger than the sum of its proper divisors (38005).

645779 is a wasteful number, since it uses less digits than its factorization.

645779 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 38004.

The product of its digits is 52920, while the sum is 38.

The square root of 645779 is about 803.6037580798. The cubic root of 645779 is about 86.4359957325.

The spelling of 645779 in words is "six hundred forty-five thousand, seven hundred seventy-nine".