644107428 has 18 divisors (see below), whose sum is σ = 1628160534. Its totient is φ = 214702464.

The previous prime is 644107427. The next prime is 644107447. The reversal of 644107428 is 824701446.

644107428 is a `hidden beast` number, since 644 + 1 + 0 + 7 + 4 + 2 + 8 = 666.

It can be written as a sum of positive squares in only one way, i.e., 629909604 + 14197824 = 25098^2 + 3768^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a Harshad number since it is a multiple of its sum of digits (36), and also a Moran number because the ratio is a prime number: 17891873 = 644107428 / (6 + 4 + 4 + 1 + 0 + 7 + 4 + 2 + 8).

It is a junction number, because it is equal to n+sod(n) for n = 644107392 and 644107401.

It is not an unprimeable number, because it can be changed into a prime (644107421) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 8945901 + ... + 8945972.

It is an arithmetic number, because the mean of its divisors is an integer number (90453363).

Almost surely, 2^644107428 is an apocalyptic number.

It is an amenable number.

644107428 is an abundant number, since it is smaller than the sum of its proper divisors (984053106).

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

644107428 is a wasteful number, since it uses less digits than its factorization.

644107428 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17891883 (or 17891878 counting only the distinct ones).

The product of its (nonzero) digits is 43008, while the sum is 36.

The square root of 644107428 is about 25379.2716207538. The cubic root of 644107428 is about 863.6135263559.

The spelling of 644107428 in words is "six hundred forty-four million, one hundred seven thousand, four hundred twenty-eight".