21275 has 12 divisors (see below), whose sum is σ = 28272. Its totient is φ = 15840.

The previous prime is 21269. The next prime is 21277. The reversal of 21275 is 57212.

21275 = T₃₁ + T₃₂ + ... + T₅₃.

It is not a de Polignac number, because 21275 - 2⁶ = 21211 is a prime.

It is a Duffinian number.

Its product of digits (140) is a multiple of the sum of its prime factors (70).

It is not an unprimeable number, because it can be changed into a prime (21277) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 557 + ... + 593.

It is an arithmetic number, because the mean of its divisors is an integer number (2356).

2²¹²⁷⁵ is an apocalyptic number.

21275 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21275 is a deficient number, since it is larger than the sum of its proper divisors (6997).

21275 is a wasteful number, since it uses less digits than its factorization.

21275 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 70 (or 65 counting only the distinct ones).

The product of its digits is 140, while the sum is 17.

The square root of 21275 is about 145.8595214581. The cubic root of 21275 is about 27.7091491019.

Multiplying 21275 by its sum of digits (17), we get a triangular number (361675 = T₈₅₀).

Adding to 21275 its reverse (57212), we get a palindrome (78487).

Subtracting 21275 from its reverse (57212), we obtain a cube (35937 = 33³).

It can be divided in two parts, 21 and 275, that multiplied together give a palindrome (5775).

The spelling of 21275 in words is "twenty-one thousand, two hundred seventy-five".