644127640 has 64 divisors (see below), whose sum is σ = 1564738560. Its totient is φ = 237227520.

The previous prime is 644127629. The next prime is 644127697. The reversal of 644127640 is 46721446.

It is a super-2 number, since 2×644127640² = 829800833223939200, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 644127596 and 644127605.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 238377 + ... + 241063.

It is an arithmetic number, because the mean of its divisors is an integer number (24449040).

Almost surely, 2^644127640 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 644127640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (782369280).

644127640 is an abundant number, since it is smaller than the sum of its proper divisors (920610920).

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

644127640 is a wasteful number, since it uses less digits than its factorization.

644127640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3172 (or 3168 counting only the distinct ones).

The product of its (nonzero) digits is 32256, while the sum is 34.

The square root of 644127640 is about 25379.6698166071. The cubic root of 644127640 is about 863.6225596182.

The spelling of 644127640 in words is "six hundred forty-four million, one hundred twenty-seven thousand, six hundred forty".