644001036521 has 16 divisors (see below), whose sum is σ = 690298750800. Its totient is φ = 600754223104.

The previous prime is 644001036493. The next prime is 644001036529. The reversal of 644001036521 is 125630100446.

It can be written as a sum of positive squares in 8 ways, for example, as 151006074025 + 492994962496 = 388595^2 + 702136^2 .

It is not a de Polignac number, because 644001036521 - 2⁶ = 644001036457 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644001036529) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 24836 + ... + 1135173.

It is an arithmetic number, because the mean of its divisors is an integer number (43143671925).

Almost surely, 2^644001036521 is an apocalyptic number.

It is an amenable number.

644001036521 is a deficient number, since it is larger than the sum of its proper divisors (46297714279).

644001036521 is a wasteful number, since it uses less digits than its factorization.

644001036521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1160173 (or 1160139 counting only the distinct ones).

The product of its (nonzero) digits is 17280, while the sum is 32.

Adding to 644001036521 its reverse (125630100446), we get a palindrome (769631136967).

The spelling of 644001036521 in words is "six hundred forty-four billion, one million, thirty-six thousand, five hundred twenty-one".