21161 has 4 divisors (see below), whose sum is σ = 24192. Its totient is φ = 18132.

The previous prime is 21157. The next prime is 21163. The reversal of 21161 is 16112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21161 - 2² = 21157 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21163) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1505 + ... + 1518.

It is an arithmetic number, because the mean of its divisors is an integer number (6048).

2²¹¹⁶¹ is an apocalyptic number.

It is an amenable number.

21161 is a deficient number, since it is larger than the sum of its proper divisors (3031).

21161 is an equidigital number, since it uses as much as digits as its factorization.

21161 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3030.

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

The square root of 21161 is about 145.4682095855. The cubic root of 21161 is about 27.6595681858.

Adding to 21161 its reverse (16112), we get a palindrome (37273).

It can be divided in two parts, 211 and 61, that added together give a palindrome (272).

The spelling of 21161 in words is "twenty-one thousand, one hundred sixty-one".