644540 has 48 divisors (see below), whose sum is σ = 1519392. Its totient is φ = 228096.

The previous prime is 644531. The next prime is 644549. The reversal of 644540 is 45446.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (644531) and next prime (644549).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644549) 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, 9587 + ... + 9653.

It is an arithmetic number, because the mean of its divisors is an integer number (31654).

2⁶⁴⁴⁵⁴⁰ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (759696).

644540 is an abundant number, since it is smaller than the sum of its proper divisors (874852).

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

644540 is a wasteful number, since it uses less digits than its factorization.

644540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 126 (or 124 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 23.

The square root of 644540 is about 802.8324856407. The cubic root of 644540 is about 86.3806812660.

Adding to 644540 its reverse (45446), we get a palindrome (689986).

The spelling of 644540 in words is "six hundred forty-four thousand, five hundred forty".