521640 has 160 divisors (see below), whose sum is σ = 2090880. Its totient is φ = 114048.

The previous prime is 521603. The next prime is 521641. The reversal of 521640 is 46125.

It is a happy number.

521640 is a `hidden beast` number, since 5 + 21 + 640 = 666.

521640 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (521641) by changing a digit.

521640 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 22669 + ... + 22691.

It is an arithmetic number, because the mean of its divisors is an integer number (13068).

2⁵²¹⁶⁴⁰ 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 521640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1045440).

521640 is an abundant number, since it is smaller than the sum of its proper divisors (1569240).

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

521640 is a wasteful number, since it uses less digits than its factorization.

521640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 53 (or 40 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 521640 is about 722.2464953186. The cubic root of 521640 is about 80.4989647900.

Adding to 521640 its reverse (46125), we get a palindrome (567765).

The spelling of 521640 in words is "five hundred twenty-one thousand, six hundred forty".