21556993 has 4 divisors (see below), whose sum is σ = 21581568. Its totient is φ = 21532420.

The previous prime is 21556987. The next prime is 21556999. The reversal of 21556993 is 39965512.

It is a happy number.

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 an interprime number because it is at equal distance from previous prime (21556987) and next prime (21556999).

It is a cyclic number.

It is not a de Polignac number, because 21556993 - 2⁵ = 21556961 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21556999) 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, 10921 + ... + 12742.

It is an arithmetic number, because the mean of its divisors is an integer number (5395392).

Almost surely, 2^21556993 is an apocalyptic number.

It is an amenable number.

21556993 is a deficient number, since it is larger than the sum of its proper divisors (24575).

21556993 is an equidigital number, since it uses as much as digits as its factorization.

21556993 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24574.

The product of its digits is 72900, while the sum is 40.

The square root of 21556993 is about 4642.9508935590. The cubic root of 21556993 is about 278.3103731245.

The spelling of 21556993 in words is "twenty-one million, five hundred fifty-six thousand, nine hundred ninety-three".