21123 has 6 divisors (see below), whose sum is σ = 30524.
Its totient is φ = 14076.
The previous prime is 21121. The next prime is 21139. The reversal of 21123 is 32112.
Adding to 21123 its reverse (32112), we get a palindrome (53235).
It can be divided in two parts, 2112 and 3, that multiplied together give a palindrome (6336).
It is a happy number.
It is not a de Polignac number, because 21123 - 21 = 21121 is a prime.
It is a super-2 number, since 2×211232 = 892362258, which contains 22 as substring.
It is a Harshad number since it is a multiple of its sum of digits (9), and also a Moran number because the ratio is a prime number: 2347 = 21123 / (2 + 1 + 1 + 2 + 3).
It is a Duffinian number.
It is a plaindrome in base 14.
It is not an unprimeable number, because it can be changed into a prime (21121) by changing a digit.
It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1165 + ... + 1182.
221123 is an apocalyptic number.
21123 is a deficient number, since it is larger than the sum of its proper divisors (9401).
21123 is a wasteful number, since it uses less digits than its factorization.
21123 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 2353 (or 2350 counting only the distinct ones).
The product of its digits is 12, while the sum is 9.
The square root of 21123 is about 145.3375381655.
The cubic root of 21123 is about 27.6430016504.
The spelling of 21123 in words is "twenty-one thousand, one hundred twenty-three", and thus it is an iban number.