21175 has 18 divisors (see below), whose sum is σ = 32984. Its totient is φ = 13200.

The previous prime is 21169. The next prime is 21179. The reversal of 21175 is 57112.

21175 = T₃₄ + T₃₅ + ... + T₅₄.

It is not a de Polignac number, because 21175 - 2⁵ = 21143 is a prime.

21175 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21179) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 1920 + ... + 1930.

21175 is a Friedman number, since it can be written as 7*(11*5)^2, using all its digits and the basic arithmetic operations.

2²¹¹⁷⁵ is an apocalyptic number.

21175 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21175 is a deficient number, since it is larger than the sum of its proper divisors (11809).

21175 is a wasteful number, since it uses less digits than its factorization.

21175 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 39 (or 23 counting only the distinct ones).

The product of its digits is 70, while the sum is 16.

The square root of 21175 is about 145.5163221086. The cubic root of 21175 is about 27.6656666466.

Adding to 21175 its reverse (57112), we get a palindrome (78287).

Subtracting 21175 from its reverse (57112), we obtain a cube (35937 = 33³).

It can be divided in two parts, 2117 and 5, that multiplied together give a triangular number (10585 = T₁₄₅).

The spelling of 21175 in words is "twenty-one thousand, one hundred seventy-five".