21356 has 12 divisors (see below), whose sum is σ = 39480. Its totient is φ = 10080.

The previous prime is 21347. The next prime is 21377. The reversal of 21356 is 65312.

21356 is nontrivially palindromic in base 5.

It is an unprimeable number.

21356 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 65 + ... + 216.

It is an arithmetic number, because the mean of its divisors is an integer number (3290).

2²¹³⁵⁶ is an apocalyptic number.

It is an amenable number.

21356 is a deficient number, since it is larger than the sum of its proper divisors (18124).

21356 is a wasteful number, since it uses less digits than its factorization.

21356 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 304 (or 302 counting only the distinct ones).

The product of its digits is 180, while the sum is 17.

The square root of 21356 is about 146.1369220971. The cubic root of 21356 is about 27.7442701153.

Adding to 21356 its reverse (65312), we get a palindrome (86668).

Subtracting 21356 from its reverse (65312), we obtain a triangular number (43956 = T₂₉₆).

The spelling of 21356 in words is "twenty-one thousand, three hundred fifty-six".