21005533 has 4 divisors (see below), whose sum is σ = 21349948. Its totient is φ = 20661120.

The previous prime is 21005503. The next prime is 21005539. The reversal of 21005533 is 33550012.

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 2022084 + 18983449 = 1422^2 + 4357^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21005533 is a prime.

It is a super-2 number, since 2×21005533² = 882464833228178, which contains 22 as substring.

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 21005533.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005539) 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, 172116 + ... + 172237.

It is an arithmetic number, because the mean of its divisors is an integer number (5337487).

Almost surely, 2^21005533 is an apocalyptic number.

It is an amenable number.

21005533 is a deficient number, since it is larger than the sum of its proper divisors (344415).

21005533 is an equidigital number, since it uses as much as digits as its factorization.

21005533 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 344414.

The product of its (nonzero) digits is 450, while the sum is 19.

The square root of 21005533 is about 4583.1793549893. The cubic root of 21005533 is about 275.9166458714.

Adding to 21005533 its reverse (33550012), we get a palindrome (54555545).

The spelling of 21005533 in words is "twenty-one million, five thousand, five hundred thirty-three".