217920 has 56 divisors (see below), whose sum is σ = 694944. Its totient is φ = 57856.

The previous prime is 217909. The next prime is 217933. The reversal of 217920 is 29712.

It is a happy number.

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 an Ulam number.

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 217920.

It is an unprimeable number.

217920 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, 847 + ... + 1073.

2²¹⁷⁹²⁰ is an apocalyptic number.

217920 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 217920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (347472).

217920 is an abundant number, since it is smaller than the sum of its proper divisors (477024).

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

217920 is a wasteful number, since it uses less digits than its factorization.

217920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 247 (or 237 counting only the distinct ones).

The product of its (nonzero) digits is 252, while the sum is 21.

The square root of 217920 is about 466.8190227486. The cubic root of 217920 is about 60.1772536147.

The spelling of 217920 in words is "two hundred seventeen thousand, nine hundred twenty".