644661504 has 216 divisors, whose sum is σ = 1980570592. Its totient is φ = 209018880.

The previous prime is 644661499. The next prime is 644661517. The reversal of 644661504 is 405166446.

644661504 is a `hidden beast` number, since 644 + 6 + 6 + 1 + 5 + 0 + 4 = 666.

It is a tau number, because it is divible by the number of its divisors (216).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 2674824 + ... + 2675064.

Almost surely, 2^644661504 is an apocalyptic number.

644661504 is a gapful number since it is divisible by the number (64) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644661504, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (990285296).

644661504 is an abundant number, since it is smaller than the sum of its proper divisors (1335909088).

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

644661504 is an equidigital number, since it uses as much as digits as its factorization.

644661504 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 315 (or 289 counting only the distinct ones).

The product of its (nonzero) digits is 69120, while the sum is 36.

The square root of 644661504 is about 25390.1851903447. The cubic root of 644661504 is about 863.8610887786.

The spelling of 644661504 in words is "six hundred forty-four million, six hundred sixty-one thousand, five hundred four".