20918 has 4 divisors (see below), whose sum is σ = 31380. Its totient is φ = 10458.

The previous prime is 20903. The next prime is 20921. The reversal of 20918 is 81902.

It is a semiprime because it is the product of two primes.

It is a self number, because there is not a number n which added to its sum of digits gives 20918.

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 20918.

It is an unprimeable number.

20918 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 as a sum of consecutive naturals, namely, 5228 + ... + 5231.

It is an arithmetic number, because the mean of its divisors is an integer number (7845).

2²⁰⁹¹⁸ is an apocalyptic number.

20918 is a deficient number, since it is larger than the sum of its proper divisors (10462).

20918 is a wasteful number, since it uses less digits than its factorization.

20918 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10461.

The product of its (nonzero) digits is 144, while the sum is 20.

The square root of 20918 is about 144.6305638515. The cubic root of 20918 is about 27.5532851157.

The spelling of 20918 in words is "twenty thousand, nine hundred eighteen".