644540544 has 256 divisors, whose sum is σ = 2019600000. Its totient is φ = 202051584.

The previous prime is 644540537. The next prime is 644540557. The reversal of 644540544 is 445045446.

644540544 is a `hidden beast` number, since 64 + 4 + 54 + 0 + 544 = 666.

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

It is a junction number, because it is equal to n+sod(n) for n = 644540499 and 644540508.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 5913162 + ... + 5913270.

Almost surely, 2^644540544 is an apocalyptic number.

644540544 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 644540544, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1009800000).

644540544 is an abundant number, since it is smaller than the sum of its proper divisors (1375059456).

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

644540544 is a wasteful number, since it uses less digits than its factorization.

644540544 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 220 (or 202 counting only the distinct ones).

The product of its (nonzero) digits is 153600, while the sum is 36.

The square root of 644540544 is about 25387.8030557983. The cubic root of 644540544 is about 863.8070556812.

The spelling of 644540544 in words is "six hundred forty-four million, five hundred forty thousand, five hundred forty-four".