644240 has 20 divisors (see below), whose sum is σ = 1498044. Its totient is φ = 257664.

The previous prime is 644239. The next prime is 644257. The reversal of 644240 is 42446.

It can be written as a sum of positive squares in 2 ways, for example, as 369664 + 274576 = 608^2 + 524^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a Harshad number since it is a multiple of its sum of digits (20).

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 644240.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3947 + ... + 4106.

2⁶⁴⁴²⁴⁰ is an apocalyptic number.

It is an amenable number.

644240 is an abundant number, since it is smaller than the sum of its proper divisors (853804).

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

644240 is a wasteful number, since it uses less digits than its factorization.

644240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8066 (or 8060 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 20.

The square root of 644240 is about 802.6456254163. The cubic root of 644240 is about 86.3672772745.

Adding to 644240 its reverse (42446), we get a palindrome (686686).

The spelling of 644240 in words is "six hundred forty-four thousand, two hundred forty".