21545553 has 4 divisors (see below), whose sum is σ = 28727408. Its totient is φ = 14363700.

The previous prime is 21545551. The next prime is 21545603. The reversal of 21545553 is 35554512.

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 not a de Polignac number, because 21545553 - 2¹ = 21545551 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21545553.

It is not an unprimeable number, because it can be changed into a prime (21545551) 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, 3590923 + ... + 3590928.

It is an arithmetic number, because the mean of its divisors is an integer number (7181852).

Almost surely, 2^21545553 is an apocalyptic number.

It is an amenable number.

21545553 is a deficient number, since it is larger than the sum of its proper divisors (7181855).

21545553 is an equidigital number, since it uses as much as digits as its factorization.

21545553 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7181854.

The product of its digits is 15000, while the sum is 30.

The square root of 21545553 is about 4641.7187549441. The cubic root of 21545553 is about 278.2611325826.

The spelling of 21545553 in words is "twenty-one million, five hundred forty-five thousand, five hundred fifty-three".