640240 has 40 divisors (see below), whose sum is σ = 1526688. Its totient is φ = 249600.

The previous prime is 640231. The next prime is 640247. The reversal of 640240 is 42046.

It is a tau number, because it is divible by the number of its divisors (40).

It is a Harshad number since it is a multiple of its sum of digits (16).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640247) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4165 + ... + 4315.

640240 is a Friedman number, since it can be written as (60+20^4)*4, using all its digits and the basic arithmetic operations.

2⁶⁴⁰²⁴⁰ 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 640240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (763344).

640240 is an abundant number, since it is smaller than the sum of its proper divisors (886448).

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

640240 is a wasteful number, since it uses less digits than its factorization.

640240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 217 (or 211 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 16.

The square root of 640240 is about 800.1499859401. The cubic root of 640240 is about 86.1881584285.

Adding to 640240 its reverse (42046), we get a palindrome (682286).

The spelling of 640240 in words is "six hundred forty thousand, two hundred forty".