21536993 has 4 divisors (see below), whose sum is σ = 22473408. Its totient is φ = 20600580.

The previous prime is 21536989. The next prime is 21537001. The reversal of 21536993 is 39963512.

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 21536993 - 2² = 21536989 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21536953) 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, 468173 + ... + 468218.

It is an arithmetic number, because the mean of its divisors is an integer number (5618352).

Almost surely, 2^21536993 is an apocalyptic number.

21536993 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

It is an amenable number.

21536993 is a deficient number, since it is larger than the sum of its proper divisors (936415).

21536993 is an equidigital number, since it uses as much as digits as its factorization.

21536993 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 936414.

The product of its digits is 43740, while the sum is 38.

The square root of 21536993 is about 4640.7965911037. The cubic root of 21536993 is about 278.2242768595.

The spelling of 21536993 in words is "twenty-one million, five hundred thirty-six thousand, nine hundred ninety-three".