21481 has 2 divisors, whose sum is σ = 21482. Its totient is φ = 21480.

The previous prime is 21467. The next prime is 21487. The reversal of 21481 is 18412.

It is a happy number.

21481 is nontrivially palindromic in base 5.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19881 + 1600 = 141^2 + 40^2 .

It is a cyclic number.

It is not a de Polignac number, because 21481 - 2¹¹ = 19433 is a prime.

It is a super-2 number, since 2×21481² = 922866722, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21487) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10740 + 10741.

It is an arithmetic number, because the mean of its divisors is an integer number (10741).

2²¹⁴⁸¹ is an apocalyptic number.

It is an amenable number.

21481 is a deficient number, since it is larger than the sum of its proper divisors (1).

21481 is an equidigital number, since it uses as much as digits as its factorization.

21481 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 64, while the sum is 16.

The square root of 21481 is about 146.5639792036. The cubic root of 21481 is about 27.7982953598.

Adding to 21481 its reverse (18412), we get a palindrome (39893).

It can be divided in two parts, 21 and 481, that multiplied together give a palindrome (10101).

The spelling of 21481 in words is "twenty-one thousand, four hundred eighty-one".