21840043 has 4 divisors (see below), whose sum is σ = 21856528. Its totient is φ = 21823560.

The previous prime is 21840029. The next prime is 21840047. The reversal of 21840043 is 34004812.

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 21840043 - 2¹³ = 21831851 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21839996 and 21840023.

It is not an unprimeable number, because it can be changed into a prime (21840047) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6063 + ... + 8968.

It is an arithmetic number, because the mean of its divisors is an integer number (5464132).

Almost surely, 2^21840043 is an apocalyptic number.

21840043 is a deficient number, since it is larger than the sum of its proper divisors (16485).

21840043 is a wasteful number, since it uses less digits than its factorization.

21840043 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16484.

The product of its (nonzero) digits is 768, while the sum is 22.

The square root of 21840043 is about 4673.3331787922. Note that the first 3 decimals coincide. The cubic root of 21840043 is about 279.5231808202.

Adding to 21840043 its reverse (34004812), we get a palindrome (55844855).

The spelling of 21840043 in words is "twenty-one million, eight hundred forty thousand, forty-three".