645440 has 28 divisors (see below), whose sum is σ = 1537716. Its totient is φ = 258048.

The previous prime is 645433. The next prime is 645443. The reversal of 645440 is 44546.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 399424 + 246016 = 632^2 + 496^2 .

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 645440.

It is not an unprimeable number, because it can be changed into a prime (645443) 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, 689 + ... + 1328.

2⁶⁴⁵⁴⁴⁰ is an apocalyptic number.

It is an amenable number.

645440 is an abundant number, since it is smaller than the sum of its proper divisors (892276).

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

645440 is a wasteful number, since it uses less digits than its factorization.

645440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2034 (or 2024 counting only the distinct ones).

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

The square root of 645440 is about 803.3928055441. The cubic root of 645440 is about 86.4208683017.

Adding to 645440 its reverse (44546), we get a palindrome (689986).

The spelling of 645440 in words is "six hundred forty-five thousand, four hundred forty".