21243553 has 4 divisors (see below), whose sum is σ = 21268548. Its totient is φ = 21218560.

The previous prime is 21243533. The next prime is 21243581. The reversal of 21243553 is 35534212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 8690704 + 12552849 = 2948^2 + 3543^2 .

It is a cyclic number.

It is not a de Polignac number, because 21243553 - 2²¹ = 19146401 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21243503) 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, 11176 + ... + 12937.

It is an arithmetic number, because the mean of its divisors is an integer number (5317137).

Almost surely, 2^21243553 is an apocalyptic number.

It is an amenable number.

21243553 is a deficient number, since it is larger than the sum of its proper divisors (24995).

21243553 is an equidigital number, since it uses as much as digits as its factorization.

21243553 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24994.

The product of its digits is 3600, while the sum is 25.

The square root of 21243553 is about 4609.0729002696. The cubic root of 21243553 is about 276.9548988855.

Adding to 21243553 its reverse (35534212), we get a palindrome (56777765).

The spelling of 21243553 in words is "twenty-one million, two hundred forty-three thousand, five hundred fifty-three".