644204020 has 12 divisors (see below), whose sum is σ = 1352828484. Its totient is φ = 257681600.

The previous prime is 644204017. The next prime is 644204023. The reversal of 644204020 is 20402446.

It is an interprime number because it is at equal distance from previous prime (644204017) and next prime (644204023).

It can be written as a sum of positive squares in 2 ways, for example, as 448931344 + 195272676 = 21188^2 + 13974^2 .

It is a junction number, because it is equal to n+sod(n) for n = 644203982 and 644204000.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644204023) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16105081 + ... + 16105120.

It is an arithmetic number, because the mean of its divisors is an integer number (112735707).

Almost surely, 2^644204020 is an apocalyptic number.

It is an amenable number.

644204020 is an abundant number, since it is smaller than the sum of its proper divisors (708624464).

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

644204020 is a wasteful number, since it uses less digits than its factorization.

644204020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32210210 (or 32210208 counting only the distinct ones).

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

The square root of 644204020 is about 25381.1745197105. The cubic root of 644204020 is about 863.6566940971.

Adding to 644204020 its reverse (20402446), we get a palindrome (664606466).

The spelling of 644204020 in words is "six hundred forty-four million, two hundred four thousand, twenty".