21493993 has 4 divisors (see below), whose sum is σ = 21951360. Its totient is φ = 21036628.

The previous prime is 21493957. The next prime is 21493999. The reversal of 21493993 is 39939412.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21493993 - 2⁹ = 21493481 is a prime.

It is a Smith number, since the sum of its digits (40) 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 (21493999) 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, 228613 + ... + 228706.

It is an arithmetic number, because the mean of its divisors is an integer number (5487840).

Almost surely, 2^21493993 is an apocalyptic number.

It is an amenable number.

21493993 is a deficient number, since it is larger than the sum of its proper divisors (457367).

21493993 is an equidigital number, since it uses as much as digits as its factorization.

21493993 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 457366.

The product of its digits is 52488, while the sum is 40.

The square root of 21493993 is about 4636.1614510282. The cubic root of 21493993 is about 278.0389892351.

The spelling of 21493993 in words is "twenty-one million, four hundred ninety-three thousand, nine hundred ninety-three".