1644656813 has 4 divisors (see below), whose sum is σ = 1644795900. Its totient is φ = 1644517728.

The previous prime is 1644656749. The next prime is 1644656843. The reversal of 1644656813 is 3186564461.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 552156004 + 1092500809 = 23498^2 + 33053^2 .

It is a cyclic number.

It is not a de Polignac number, because 1644656813 - 2⁶ = 1644656749 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 (1644656843) 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, 49970 + ... + 76067.

It is an arithmetic number, because the mean of its divisors is an integer number (411198975).

Almost surely, 2^1644656813 is an apocalyptic number.

It is an amenable number.

1644656813 is a deficient number, since it is larger than the sum of its proper divisors (139087).

1644656813 is a wasteful number, since it uses less digits than its factorization.

1644656813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 139086.

The product of its digits is 414720, while the sum is 44.

The square root of 1644656813 is about 40554.3686056139. The cubic root of 1644656813 is about 1180.3888436501.

The spelling of 1644656813 in words is "one billion, six hundred forty-four million, six hundred fifty-six thousand, eight hundred thirteen".