644293440 has 560 divisors, whose sum is σ = 2708525952. Its totient is φ = 142331904.

The previous prime is 644293423. The next prime is 644293459. The reversal of 644293440 is 44392446.

644293440 is a `hidden beast` number, since 644 + 2 + 9 + 3 + 4 + 4 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (560).

It is a super-2 number, since 2×644293440² = 830228073654067200, which contains 22 as substring.

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 = 644293395 and 644293404.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 9616287 + ... + 9616353.

Almost surely, 2^644293440 is an apocalyptic number.

644293440 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 644293440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1354262976).

644293440 is an abundant number, since it is smaller than the sum of its proper divisors (2064232512).

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

644293440 is a wasteful number, since it uses less digits than its factorization.

644293440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 156 (or 137 counting only the distinct ones).

The product of its (nonzero) digits is 82944, while the sum is 36.

The square root of 644293440 is about 25382.9360003921. The cubic root of 644293440 is about 863.6966527676.

The spelling of 644293440 in words is "six hundred forty-four million, two hundred ninety-three thousand, four hundred forty".