644581 has 4 divisors (see below), whose sum is σ = 736672. Its totient is φ = 552492.

The previous prime is 644569. The next prime is 644593. The reversal of 644581 is 185446.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 185446 = 2 ⋅92723.

It is an interprime number because it is at equal distance from previous prime (644569) and next prime (644593).

It is a cyclic number.

It is not a de Polignac number, because 644581 - 2⁵ = 644549 is a prime.

It is a super-2 number, since 2×644581² = 830969331122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644531) 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, 46035 + ... + 46048.

It is an arithmetic number, because the mean of its divisors is an integer number (184168).

2⁶⁴⁴⁵⁸¹ is an apocalyptic number.

It is an amenable number.

644581 is a deficient number, since it is larger than the sum of its proper divisors (92091).

644581 is an equidigital number, since it uses as much as digits as its factorization.

644581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 92090.

The product of its digits is 3840, while the sum is 28.

The square root of 644581 is about 802.8580198267. The cubic root of 644581 is about 86.3825128218.

It can be divided in two parts, 644 and 581, that added together give a triangular number (1225 = T₄₉).

The spelling of 644581 in words is "six hundred forty-four thousand, five hundred eighty-one".