644973264 has 120 divisors (see below), whose sum is σ = 1961723400. Its totient is φ = 196632576.

The previous prime is 644973257. The next prime is 644973269. The reversal of 644973264 is 462379446.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 77580864 + 567392400 = 8808^2 + 23820^2 .

It is a super-2 number, since 2×644973264² = 831981022549627392, which contains 22 as substring.

It is a zygodrome in base 3.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644973269) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 210012 + ... + 213060.

It is an arithmetic number, because the mean of its divisors is an integer number (16347695).

Almost surely, 2^644973264 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 644973264, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (980861700).

644973264 is an abundant number, since it is smaller than the sum of its proper divisors (1316750136).

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

644973264 is a wasteful number, since it uses less digits than its factorization.

644973264 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3189 (or 3180 counting only the distinct ones).

The product of its digits is 870912, while the sum is 45.

The square root of 644973264 is about 25396.3238284599. The cubic root of 644973264 is about 864.0003215019. Note that the first 3 decimals are identical.

The spelling of 644973264 in words is "six hundred forty-four million, nine hundred seventy-three thousand, two hundred sixty-four".