21331553 has 4 divisors (see below), whose sum is σ = 21407748. Its totient is φ = 21255360.

The previous prime is 21331543. The next prime is 21331567. The reversal of 21331553 is 35513312.

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 15460624 + 5870929 = 3932^2 + 2423^2 .

It is a cyclic number.

It is not a de Polignac number, because 21331553 - 2⁴ = 21331537 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21331523) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 37676 + ... + 38237.

It is an arithmetic number, because the mean of its divisors is an integer number (5351937).

Almost surely, 2^21331553 is an apocalyptic number.

It is an amenable number.

21331553 is a deficient number, since it is larger than the sum of its proper divisors (76195).

21331553 is an equidigital number, since it uses as much as digits as its factorization.

21331553 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 76194.

The product of its digits is 1350, while the sum is 23.

The square root of 21331553 is about 4618.6094227592. The cubic root of 21331553 is about 277.3367944369.

Adding to 21331553 its reverse (35513312), we get a palindrome (56844865).

The spelling of 21331553 in words is "twenty-one million, three hundred thirty-one thousand, five hundred fifty-three".