21279 has 8 divisors (see below), whose sum is σ = 29232. Its totient is φ = 13760.

The previous prime is 21277. The next prime is 21283. The reversal of 21279 is 97212.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21279 - 2¹ = 21277 is a prime.

It is an Ulam number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21277) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 37 + ... + 209.

It is an arithmetic number, because the mean of its divisors is an integer number (3654).

2²¹²⁷⁹ is an apocalyptic number.

21279 is a deficient number, since it is larger than the sum of its proper divisors (7953).

21279 is a wasteful number, since it uses less digits than its factorization.

21279 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 217.

The product of its digits is 252, while the sum is 21.

The square root of 21279 is about 145.8732326371. The cubic root of 21279 is about 27.7108855634.

It can be divided in two parts, 21 and 279, that added together give a triangular number (300 = T₂₄).

The spelling of 21279 in words is "twenty-one thousand, two hundred seventy-nine".