21101 has 2 divisors, whose sum is σ = 21102. Its totient is φ = 21100.

The previous prime is 21089. The next prime is 21107. The reversal of 21101 is 10112.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15625 + 5476 = 125^2 + 74^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21101 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21107) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10550 + 10551.

It is an arithmetic number, because the mean of its divisors is an integer number (10551).

2²¹¹⁰¹ is an apocalyptic number.

It is an amenable number.

21101 is a deficient number, since it is larger than the sum of its proper divisors (1).

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 product of its (nonzero) digits is 2, while the sum is 5.

The square root of 21101 is about 145.2618325645. The cubic root of 21101 is about 27.6334014154.

Adding to 21101 its reverse (10112), we get a palindrome (31213).

Multiplying 21101 by its reverse (10112), we get a palindrome (213373312).

The spelling of 21101 in words is "twenty-one thousand, one hundred one", and thus it is an iban number.