644779 has 4 divisors (see below), whose sum is σ = 649984. Its totient is φ = 639576.

The previous prime is 644767. The next prime is 644783. The reversal of 644779 is 977446.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 977446 = 2 ⋅488723.

It is a cyclic number.

It is not a de Polignac number, because 644779 - 2⁵ = 644747 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644729) 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, 2412 + ... + 2665.

It is an arithmetic number, because the mean of its divisors is an integer number (162496).

2⁶⁴⁴⁷⁷⁹ is an apocalyptic number.

644779 is a deficient number, since it is larger than the sum of its proper divisors (5205).

644779 is a wasteful number, since it uses less digits than its factorization.

644779 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5204.

The product of its digits is 42336, while the sum is 37.

The square root of 644779 is about 802.9813198325. The cubic root of 644779 is about 86.3913568029.

The spelling of 644779 in words is "six hundred forty-four thousand, seven hundred seventy-nine".