21090043 has 4 divisors (see below), whose sum is σ = 22712368. Its totient is φ = 19467720.

The previous prime is 21090007. The next prime is 21090061. The reversal of 21090043 is 34009012.

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 21090043 - 2⁹ = 21089531 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21090043.

It is not an unprimeable number, because it can be changed into a prime (21090073) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 811143 + ... + 811168.

It is an arithmetic number, because the mean of its divisors is an integer number (5678092).

Almost surely, 2^21090043 is an apocalyptic number.

21090043 is a deficient number, since it is larger than the sum of its proper divisors (1622325).

21090043 is a wasteful number, since it uses less digits than its factorization.

21090043 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1622324.

The product of its (nonzero) digits is 216, while the sum is 19.

The square root of 21090043 is about 4592.3896829429. The cubic root of 21090043 is about 276.2861757256.

Adding to 21090043 its reverse (34009012), we get a palindrome (55099055).

The spelling of 21090043 in words is "twenty-one million, ninety thousand, forty-three".