21011 has 2 divisors, whose sum is σ = 21012.
Its totient is φ = 21010.
The previous prime is 21001. The next prime is 21013. The reversal of 21011 is 11012.
Adding to 21011 its reverse (11012), we get a palindrome (32023).
Subtracting from 21011 its reverse (11012), we obtain a palindrome (9999).
Multipling 21011 by its reverse (11012), we get a palindrome (231373132).
It is a happy number.
It is a strong prime.
It is a cyclic number.
It is not a de Polignac number, because 21011 - 26 = 20947 is a prime.
It is a Sophie Germain prime.
Together with 21013, it forms a pair of twin primes.
It is a Chen prime.
It is a nialpdrome in base 13.
It is a junction number, because it is equal to n+sod(n) for n = 20986 and 21004.
It is not a weakly prime, because it can be changed into another prime (21013) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10505 + 10506.
It is an arithmetic number, because the mean of its divisors is an integer number (10506).
221011 is an apocalyptic number.
21011 is a deficient number, since it is larger than the sum of its proper divisors (1).
21011 is an equidigital number, since it uses as much as digits as its factorization.
21011 is an evil number, because the sum of its binary digits is even.
The product of its (nonzero) digits is 2, while the sum is 5.
The square root of 21011 is about 144.9517160988.
The cubic root of 21011 is about 27.5940580922.
The spelling of 21011 in words is "twenty-one thousand, eleven", and thus it is an iban number.