21611 has 2 divisors, whose sum is σ = 21612. Its totient is φ = 21610.

The previous prime is 21601. The next prime is 21613. The reversal of 21611 is 11612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21611 - 2¹⁴ = 5227 is a prime.

It is a Sophie Germain prime.

Together with 21613, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21592 and 21601.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21611.

It is not a weakly prime, because it can be changed into another prime (21613) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10805 + 10806.

It is an arithmetic number, because the mean of its divisors is an integer number (10806).

2²¹⁶¹¹ is an apocalyptic number.

21611 is a deficient number, since it is larger than the sum of its proper divisors (1).

21611 is an equidigital number, since it uses as much as digits as its factorization.

21611 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12, while the sum is 11.

The square root of 21611 is about 147.0068025637. The cubic root of 21611 is about 27.8542597436.

Subtracting from 21611 its reverse (11612), we obtain a palindrome (9999).

The spelling of 21611 in words is "twenty-one thousand, six hundred eleven".