644956816 has 45 divisors (see below), whose sum is σ = 1455225219. Its totient is φ = 276105312.

The previous prime is 644956813. The next prime is 644956847. The reversal of 644956816 is 618659446.

The square root of 644956816 is 25396.

It is a perfect power (a square), and thus also a powerful number.

It is a Harshad number since it is a multiple of its sum of digits (49).

It is a self number, because there is not a number n which added to its sum of digits gives 644956816.

It is not an unprimeable number, because it can be changed into a prime (644956813) 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 8 ways as a sum of consecutive naturals, for example, 710635 + ... + 711541.

Almost surely, 2^644956816 is an apocalyptic number.

644956816 is the 25396-th square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644956816

644956816 is an abundant number, since it is smaller than the sum of its proper divisors (810268403).

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

644956816 is an frugal number, since it uses more digits than its factorization.

644956816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1836 (or 916 counting only the distinct ones).

The product of its digits is 1244160, while the sum is 49.

The cubic root of 644956816 is about 863.9929769091.

Multiplying 644956816 by its sum of digits (49), we get a square (31602883984 = 177772²).

644956816 divided by its sum of digits (49) gives a square (13162384 = 3628²).

The spelling of 644956816 in words is "six hundred forty-four million, nine hundred fifty-six thousand, eight hundred sixteen".