644778 has 24 divisors (see below), whose sum is σ = 1413828. Its totient is φ = 212352.

The previous prime is 644767. The next prime is 644783. The reversal of 644778 is 877446.

It is a happy number.

644778 is a `hidden beast` number, since 644 + 7 + 7 + 8 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 439569 + 205209 = 663^2 + 453^2 .

It is a Curzon number.

It is an unprimeable number.

644778 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 in 11 ways as a sum of consecutive naturals, for example, 1876 + ... + 2192.

2⁶⁴⁴⁷⁷⁸ is an apocalyptic number.

644778 is an abundant number, since it is smaller than the sum of its proper divisors (769050).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

644778 is a wasteful number, since it uses less digits than its factorization.

644778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 438 (or 435 counting only the distinct ones).

The product of its digits is 37632, while the sum is 36.

The square root of 644778 is about 802.9806971528. The cubic root of 644778 is about 86.3913121408.

The spelling of 644778 in words is "six hundred forty-four thousand, seven hundred seventy-eight".