21043 has 4 divisors (see below), whose sum is σ = 22968. Its totient is φ = 19120.

The previous prime is 21031. The next prime is 21059. The reversal of 21043 is 34012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21043 - 2⁵ = 21011 is a prime.

21043 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (21013) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 946 + ... + 967.

It is an arithmetic number, because the mean of its divisors is an integer number (5742).

2²¹⁰⁴³ is an apocalyptic number.

21043 is a deficient number, since it is larger than the sum of its proper divisors (1925).

21043 is a wasteful number, since it uses less digits than its factorization.

21043 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1924.

The product of its (nonzero) digits is 24, while the sum is 10.

The square root of 21043 is about 145.0620556865. The cubic root of 21043 is about 27.6080596780.

Adding to 21043 its reverse (34012), we get a palindrome (55055).

It can be divided in two parts, 210 and 43, that added together give a triangular number (253 = T₂₂).

The spelling of 21043 in words is "twenty-one thousand, forty-three", and thus it is an iban number.