644444736 has 224 divisors, whose sum is σ = 1966325760. Its totient is φ = 184633344.

The previous prime is 644444729. The next prime is 644444737. The reversal of 644444736 is 637444446.

It is not an unprimeable number, because it can be changed into a prime (644444737) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 5074305 + ... + 5074431.

It is an arithmetic number, because the mean of its divisors is an integer number (8778240).

Almost surely, 2^644444736 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644444736, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (983162880).

644444736 is an abundant number, since it is smaller than the sum of its proper divisors (1321881024).

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

644444736 is a wasteful number, since it uses less digits than its factorization.

644444736 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 281 (or 271 counting only the distinct ones).

The product of its digits is 774144, while the sum is 42.

The square root of 644444736 is about 25385.9160953470. The cubic root of 644444736 is about 863.7642532395.

The spelling of 644444736 in words is "six hundred forty-four million, four hundred forty-four thousand, seven hundred thirty-six".