21133553 has 6 divisors (see below), whose sum is σ = 24583986. Its totient is φ = 18114432.

The previous prime is 21133523. The next prime is 21133559. The reversal of 21133553 is 35533112.

It can be written as a sum of positive squares in only one way, i.e., 21086464 + 47089 = 4592^2 + 217^2 .

It is not a de Polignac number, because 21133553 - 2²² = 16939249 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21133559) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 215600 + ... + 215697.

It is an arithmetic number, because the mean of its divisors is an integer number (4097331).

Almost surely, 2^21133553 is an apocalyptic number.

It is an amenable number.

21133553 is a deficient number, since it is larger than the sum of its proper divisors (3450433).

21133553 is an equidigital number, since it uses as much as digits as its factorization.

21133553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 431311 (or 431304 counting only the distinct ones).

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

The square root of 21133553 is about 4597.1244272915. The cubic root of 21133553 is about 276.4760434299.

Adding to 21133553 its reverse (35533112), we get a palindrome (56666665).

The spelling of 21133553 in words is "twenty-one million, one hundred thirty-three thousand, five hundred fifty-three".