644490 has 128 divisors (see below), whose sum is σ = 2211840. Its totient is φ = 129600.

The previous prime is 644489. The next prime is 644491. The reversal of 644490 is 94446.

644490 = 138² + 139² + ... + 165².

644490 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (644489) and next prime (644491).

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 (644491) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 20775 + ... + 20805.

It is an arithmetic number, because the mean of its divisors is an integer number (17280).

2⁶⁴⁴⁴⁹⁰ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644490, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1105920).

644490 is an abundant number, since it is smaller than the sum of its proper divisors (1567350).

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

644490 is a wasteful number, since it uses less digits than its factorization.

644490 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 65 (or 59 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 27.

The square root of 644490 is about 802.8013452904. The cubic root of 644490 is about 86.3784475563.

It can be divided in two parts, 64 and 4490, that added together give a palindrome (4554).

The spelling of 644490 in words is "six hundred forty-four thousand, four hundred ninety".