Adding to 21101 its reverse (10112), we get a palindrome (31213).
Multipling 21101 by its reverse (10112), we get a palindrome (213373312).
It is a happy number.
It is a strong prime.
It is a cyclic number.
It is a de Polignac number, because none of the positive numbers 2k-21101 is a prime.
It is a Chen prime.
It is a congruent number.
221101 is an apocalyptic number.
It is an amenable number.
21101 is an equidigital number, since it uses as much as digits as its factorization.
21101 is an evil number, because the sum of its binary digits is even.
The square root of 21101 is about 145.2618325645. The cubic root of 21101 is about 27.6334014154.
The spelling of 21101 in words is "twenty-one thousand, one hundred one", and thus it is an iban number.