21075 has 12 divisors (see below), whose sum is σ = 34968. Its totient is φ = 11200.
The previous prime is 21067. The next prime is 21089. The reversal of 21075 is 57012.
It is a happy number.
It is not a de Polignac number, because 21075 - 23 = 21067 is a prime.
It is a Harshad number since it is a multiple of its sum of digits (15).
21075 is a lucky number.
It is a zygodrome in base 5.
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 11 ways as a sum of consecutive naturals, for example, 66 + ... + 215.
It is an arithmetic number, because the mean of its divisors is an integer number (2914).
221075 is an apocalyptic number.
21075 is a gapful number since it is divisible by the number (25) formed by its first and last digit.
21075 is a deficient number, since it is larger than the sum of its proper divisors (13893).
21075 is a wasteful number, since it uses less digits than its factorization.
21075 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 294 (or 289 counting only the distinct ones).
The product of its (nonzero) digits is 70, while the sum is 15.
The square root of 21075 is about 145.1723114096. The cubic root of 21075 is about 27.6220470762.
Adding to 21075 its reverse (57012), we get a palindrome (78087).
Subtracting 21075 from its reverse (57012), we obtain a cube (35937 = 333).
It can be divided in two parts, 2107 and 5, that added together give a palindrome (2112).
The spelling of 21075 in words is "twenty-one thousand, seventy-five".
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