21255 has 16 divisors (see below), whose sum is σ = 36960. Its totient is φ = 10368.

The previous prime is 21247. The next prime is 21269. The reversal of 21255 is 55212.

It is not a de Polignac number, because 21255 - 2³ = 21247 is a prime.

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

21255 is a lucky number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21255.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 141 + ... + 249.

It is an arithmetic number, because the mean of its divisors is an integer number (2310).

2²¹²⁵⁵ is an apocalyptic number.

21255 is a deficient number, since it is larger than the sum of its proper divisors (15705).

21255 is a wasteful number, since it uses less digits than its factorization.

21255 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 130.

The product of its digits is 100, while the sum is 15.

The square root of 21255 is about 145.7909462210. The cubic root of 21255 is about 27.7004635284.

Adding to 21255 its reverse (55212), we get a palindrome (76467).

It can be divided in two parts, 21 and 255, that added together give a triangular number (276 = T₂₃).

The spelling of 21255 in words is "twenty-one thousand, two hundred fifty-five".