218640 has 40 divisors (see below), whose sum is σ = 678528. Its totient is φ = 58240.

The previous prime is 218629. The next prime is 218641. The reversal of 218640 is 46812.

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

It is a hoax number, since the sum of its digits (21) coincides with the sum of the digits of its distinct prime factors.

It is a nialpdrome in base 12.

It is not an unprimeable number, because it can be changed into a prime (218641) by changing a digit.

218640 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 216 + ... + 695.

2²¹⁸⁶⁴⁰ is an apocalyptic number.

218640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

218640 is an abundant number, since it is smaller than the sum of its proper divisors (459888).

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

218640 is a wasteful number, since it uses less digits than its factorization.

218640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 927 (or 921 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 21.

The square root of 218640 is about 467.5895636132. The cubic root of 218640 is about 60.2434552672.

Adding to 218640 its product of nonzero digits (384), we get a square (219024 = 468²).

It can be divided in two parts, 218 and 640, that added together give a palindrome (858).

The spelling of 218640 in words is "two hundred eighteen thousand, six hundred forty".