21165 has 16 divisors (see below), whose sum is σ = 36288. Its totient is φ = 10496.

The previous prime is 21163. The next prime is 21169. The reversal of 21165 is 56112.

21165 = T₆₀ + T₆₁ + ... + T₆₉.

It is a cyclic number.

It is not a de Polignac number, because 21165 - 2¹ = 21163 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a Curzon number.

It is a nialpdrome in base 13 and base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21163) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 214 + ... + 296.

It is an arithmetic number, because the mean of its divisors is an integer number (2268).

2²¹¹⁶⁵ is an apocalyptic number.

It is an amenable number.

21165 is a deficient number, since it is larger than the sum of its proper divisors (15123).

21165 is a wasteful number, since it uses less digits than its factorization.

21165 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 108.

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

The square root of 21165 is about 145.4819576442. The cubic root of 21165 is about 27.6613108776.

Adding to 21165 its reverse (56112), we get a palindrome (77277).

It can be divided in two parts, 211 and 65, that added together give a triangular number (276 = T₂₃).

The spelling of 21165 in words is "twenty-one thousand, one hundred sixty-five".