21533455 has 4 divisors (see below), whose sum is σ = 25840152. Its totient is φ = 17226760.

The previous prime is 21533443. The next prime is 21533459. The reversal of 21533455 is 55433512.

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

It is not a de Polignac number, because 21533455 - 2⁹ = 21532943 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21533459) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2153341 + ... + 2153350.

It is an arithmetic number, because the mean of its divisors is an integer number (6460038).

Almost surely, 2^21533455 is an apocalyptic number.

21533455 is a deficient number, since it is larger than the sum of its proper divisors (4306697).

21533455 is an equidigital number, since it uses as much as digits as its factorization.

21533455 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4306696.

The product of its digits is 9000, while the sum is 28.

The square root of 21533455 is about 4640.4153908891. The cubic root of 21533455 is about 278.2090408824.

Adding to 21533455 its reverse (55433512), we get a palindrome (76966967).

It can be divided in two parts, 215 and 33455, that added together give a triangular number (33670 = T₂₅₉).

The spelling of 21533455 in words is "twenty-one million, five hundred thirty-three thousand, four hundred fifty-five".