644565821386 has 16 divisors (see below), whose sum is σ = 1000229329800. Its totient is φ = 311156955648.

The previous prime is 644565821323. The next prime is 644565821399. The reversal of 644565821386 is 683128565446.

It can be written as a sum of positive squares in 4 ways, for example, as 550387418161 + 94178403225 = 741881^2 + 306885^2 .

It is a Harshad number since it is a multiple of its sum of digits (58).

It is a self number, because there is not a number n which added to its sum of digits gives 644565821386.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1285870 + ... + 1715398.

Almost surely, 2^644565821386 is an apocalyptic number.

644565821386 is a deficient number, since it is larger than the sum of its proper divisors (355663508414).

644565821386 is a wasteful number, since it uses less digits than its factorization.

644565821386 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 455433.

The product of its digits is 33177600, while the sum is 58.

The spelling of 644565821386 in words is "six hundred forty-four billion, five hundred sixty-five million, eight hundred twenty-one thousand, three hundred eighty-six".