21061 has 2 divisors, whose sum is σ = 21062. Its totient is φ = 21060.

The previous prime is 21059. The next prime is 21067. The reversal of 21061 is 16012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21025 + 36 = 145^2 + 6^2 .

It is a cyclic number.

It is not a de Polignac number, because 21061 - 2¹ = 21059 is a prime.

Together with 21059, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21067) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10530 + 10531.

It is an arithmetic number, because the mean of its divisors is an integer number (10531).

2²¹⁰⁶¹ is an apocalyptic number.

It is an amenable number.

21061 is a deficient number, since it is larger than the sum of its proper divisors (1).

21061 is an equidigital number, since it uses as much as digits as its factorization.

21061 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 12, while the sum is 10.

The square root of 21061 is about 145.1240848378. The cubic root of 21061 is about 27.6159293329.

Adding to 21061 its reverse (16012), we get a palindrome (37073).

The spelling of 21061 in words is "twenty-one thousand, sixty-one".