20518 has 4 divisors (see below), whose sum is σ = 30780. Its totient is φ = 10258.

The previous prime is 20509. The next prime is 20521. The reversal of 20518 is 81502.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 81502 = 2 ⋅40751.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5128 + ... + 5131.

It is an arithmetic number, because the mean of its divisors is an integer number (7695).

2²⁰⁵¹⁸ is an apocalyptic number.

20518 is a deficient number, since it is larger than the sum of its proper divisors (10262).

20518 is a wasteful number, since it uses less digits than its factorization.

20518 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10261.

The product of its (nonzero) digits is 80, while the sum is 16.

The square root of 20518 is about 143.2410555672. The cubic root of 20518 is about 27.3765263287.

Subtracting from 20518 its sum of digits (16), we obtain a palindrome (20502).

The spelling of 20518 in words is "twenty thousand, five hundred eighteen".