644923778 has 16 divisors (see below), whose sum is σ = 980060256. Its totient is φ = 318245280.

The previous prime is 644923771. The next prime is 644923817. The reversal of 644923778 is 877329446.

It is not an unprimeable number, because it can be changed into a prime (644923771) 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 7 ways as a sum of consecutive naturals, for example, 259550 + ... + 262022.

It is an arithmetic number, because the mean of its divisors is an integer number (61253766).

Almost surely, 2^644923778 is an apocalyptic number.

644923778 is a deficient number, since it is larger than the sum of its proper divisors (335136478).

644923778 is a wasteful number, since it uses less digits than its factorization.

644923778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4129.

The product of its digits is 2032128, while the sum is 50.

The square root of 644923778 is about 25395.3495349050. The cubic root of 644923778 is about 863.9782239382.

The spelling of 644923778 in words is "six hundred forty-four million, nine hundred twenty-three thousand, seven hundred seventy-eight".