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20911 = 111901

20911 has 4 divisors (see below), whose sum is σ = 22824. Its totient is φ = 19000.

The previous prime is 20903. The next prime is 20921. The reversal of 20911 is 11902.

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

It is a cyclic number.

It is not a de Polignac number, because 20911 - 23 = 20903 is a prime.

It is a Smith number, since the sum of its digits (13) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a pancake number, because a pancake can be divided into 20911 parts by 204 straight cuts.

It is a Duffinian number.

It is a plaindrome in base 14.

It is a junction number, because it is equal to n+sod(n) for n = 20891 and 20900.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20921) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 940 + ... + 961.

It is an arithmetic number, because the mean of its divisors is an integer number (5706).

220911 is an apocalyptic number.

20911 is a deficient number, since it is larger than the sum of its proper divisors (1913).

20911 is a wasteful number, since it uses less digits than its factorization.

20911 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1912.

The product of its (nonzero) digits is 18, while the sum is 13.

The square root of 20911 is about 144.6063622390. The cubic root of 20911 is about 27.5502112954.

Subtracting from 20911 its reverse (11902), we obtain a palindrome (9009).

The spelling of 20911 in words is "twenty thousand, nine hundred eleven".

Divisors: 1 11 1901 20911