217840 has 40 divisors (see below), whose sum is σ = 580320. Its totient is φ = 74496.

The previous prime is 217829. The next prime is 217849. The reversal of 217840 is 48712.

217840 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (217849) by changing a digit.

217840 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 7 ways as a sum of consecutive naturals, for example, 366 + ... + 754.

It is an arithmetic number, because the mean of its divisors is an integer number (14508).

2²¹⁷⁸⁴⁰ is an apocalyptic number.

217840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 217840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (290160).

217840 is an abundant number, since it is smaller than the sum of its proper divisors (362480).

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

217840 is a wasteful number, since it uses less digits than its factorization.

217840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 409 (or 403 counting only the distinct ones).

The product of its (nonzero) digits is 448, while the sum is 22.

The square root of 217840 is about 466.7333285721. The cubic root of 217840 is about 60.1698888792.

The spelling of 217840 in words is "two hundred seventeen thousand, eight hundred forty".