644553840 has 240 divisors, whose sum is σ = 2426416128. Its totient is φ = 140861952.

The previous prime is 644553839. The next prime is 644553883. The reversal of 644553840 is 48355446.

It is a tau number, because it is divible by the number of its divisors (240).

It is a super-3 number, since 3×644553840³ (a number of 27 digits) contains 333 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 269289 + ... + 271671.

Almost surely, 2^644553840 is an apocalyptic number.

644553840 is a gapful number since it is divisible by the number (60) 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 644553840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1213208064).

644553840 is an abundant number, since it is smaller than the sum of its proper divisors (1781862288).

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

644553840 is a wasteful number, since it uses less digits than its factorization.

644553840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2436 (or 2423 counting only the distinct ones).

The product of its (nonzero) digits is 230400, while the sum is 39.

The square root of 644553840 is about 25388.0649124741. The cubic root of 644553840 is about 863.8129953643.

The spelling of 644553840 in words is "six hundred forty-four million, five hundred fifty-three thousand, eight hundred forty".