21345 has 8 divisors (see below), whose sum is σ = 34176. Its totient is φ = 11376.

The previous prime is 21341. The next prime is 21347. The reversal of 21345 is 54312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21345 - 2² = 21341 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (15), and also a Moran number because the ratio is a prime number: 1423 = 21345 / (2 + 1 + 3 + 4 + 5).

It is an Ulam number.

It is a d-powerful number, because it can be written as 2⁹ + 1 + 3⁹ + 4⁵ + 5³ .

21345 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (21341) 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 7 ways as a sum of consecutive naturals, for example, 697 + ... + 726.

It is an arithmetic number, because the mean of its divisors is an integer number (4272).

2²¹³⁴⁵ is an apocalyptic number.

It is an amenable number.

21345 is a deficient number, since it is larger than the sum of its proper divisors (12831).

21345 is a wasteful number, since it uses less digits than its factorization.

21345 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1431.

The product of its digits is 120, while the sum is 15.

The square root of 21345 is about 146.0992813124. The cubic root of 21345 is about 27.7395058120.

Adding to 21345 its reverse (54312), we get a palindrome (75657).

The spelling of 21345 in words is "twenty-one thousand, three hundred forty-five".