644026221 has 20 divisors (see below), whose sum is σ = 975251772. Its totient is φ = 423465408.

The previous prime is 644026219. The next prime is 644026277. The reversal of 644026221 is 122620446.

It can be written as a sum of positive squares in 2 ways, for example, as 528356196 + 115670025 = 22986^2 + 10755^2 .

It is not a de Polignac number, because 644026221 - 2¹ = 644026219 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644026291) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 48546 + ... + 60371.

Almost surely, 2^644026221 is an apocalyptic number.

It is an amenable number.

644026221 is a deficient number, since it is larger than the sum of its proper divisors (331225551).

644026221 is a wasteful number, since it uses less digits than its factorization.

644026221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 109002 (or 108993 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 27.

The square root of 644026221 is about 25377.6717017145. The cubic root of 644026221 is about 863.5772309554.

Adding to 644026221 its reverse (122620446), we get a palindrome (766646667).

The spelling of 644026221 in words is "six hundred forty-four million, twenty-six thousand, two hundred twenty-one".