21406243 has 4 divisors (see below), whose sum is σ = 21618288. Its totient is φ = 21194200.

The previous prime is 21406241. The next prime is 21406249. The reversal of 21406243 is 34260412.

It is a happy number.

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 21406243 - 2¹ = 21406241 is a prime.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21406241) 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, 105871 + ... + 106072.

It is an arithmetic number, because the mean of its divisors is an integer number (5404572).

Almost surely, 2^21406243 is an apocalyptic number.

21406243 is a deficient number, since it is larger than the sum of its proper divisors (212045).

21406243 is a wasteful number, since it uses less digits than its factorization.

21406243 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 212044.

The product of its (nonzero) digits is 1152, while the sum is 22.

The square root of 21406243 is about 4626.6881243499. The cubic root of 21406243 is about 277.6601051035.

Adding to 21406243 its reverse (34260412), we get a palindrome (55666655).

The spelling of 21406243 in words is "twenty-one million, four hundred six thousand, two hundred forty-three".