21393 has 6 divisors (see below), whose sum is σ = 30914. Its totient is φ = 14256.

The previous prime is 21391. The next prime is 21397. The reversal of 21393 is 39312.

It can be written as a sum of positive squares in only one way, i.e., 17424 + 3969 = 132^2 + 63^2 .

It is not a de Polignac number, because 21393 - 2¹ = 21391 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21391) 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 5 ways as a sum of consecutive naturals, for example, 1180 + ... + 1197.

2²¹³⁹³ is an apocalyptic number.

It is an amenable number.

21393 is a deficient number, since it is larger than the sum of its proper divisors (9521).

21393 is a wasteful number, since it uses less digits than its factorization.

21393 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2383 (or 2380 counting only the distinct ones).

The product of its digits is 162, while the sum is 18.

The square root of 21393 is about 146.2634609190. The cubic root of 21393 is about 27.7602835030.

It can be divided in two parts, 21 and 393, that added together give a palindrome (414).

The spelling of 21393 in words is "twenty-one thousand, three hundred ninety-three".