21156 has 24 divisors (see below), whose sum is σ = 51744. Its totient is φ = 6720.

The previous prime is 21149. The next prime is 21157. The reversal of 21156 is 65112.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21156.

It is not an unprimeable number, because it can be changed into a prime (21157) 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, 471 + ... + 513.

It is an arithmetic number, because the mean of its divisors is an integer number (2156).

2²¹¹⁵⁶ is an apocalyptic number.

It is an amenable number.

21156 is an abundant number, since it is smaller than the sum of its proper divisors (30588).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25872).

21156 is a wasteful number, since it uses less digits than its factorization.

21156 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91 (or 89 counting only the distinct ones).

The product of its digits is 60, while the sum is 15.

The square root of 21156 is about 145.4510226846. The cubic root of 21156 is about 27.6573895122.

Adding to 21156 its reverse (65112), we get a palindrome (86268).

Subtracting 21156 from its reverse (65112), we obtain a triangular number (43956 = T₂₉₆).

The spelling of 21156 in words is "twenty-one thousand, one hundred fifty-six".