644240020 has 12 divisors (see below), whose sum is σ = 1352904084. Its totient is φ = 257696000.

The previous prime is 644239993. The next prime is 644240033. The reversal of 644240020 is 20042446.

It can be written as a sum of positive squares in 2 ways, for example, as 242798724 + 401441296 = 15582^2 + 20036^2 .

It is a junction number, because it is equal to n+sod(n) for n = 644239973 and 644240000.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16105981 + ... + 16106020.

It is an arithmetic number, because the mean of its divisors is an integer number (112742007).

Almost surely, 2^644240020 is an apocalyptic number.

It is an amenable number.

644240020 is an abundant number, since it is smaller than the sum of its proper divisors (708664064).

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

644240020 is a wasteful number, since it uses less digits than its factorization.

644240020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32212010 (or 32212008 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 22.

The square root of 644240020 is about 25381.8836968417. The cubic root of 644240020 is about 863.6727816826.

Adding to 644240020 its reverse (20042446), we get a palindrome (664282466).

The spelling of 644240020 in words is "six hundred forty-four million, two hundred forty thousand, twenty".