21533421 has 16 divisors (see below), whose sum is σ = 35337344. Its totient is φ = 11358144.

The previous prime is 21533363. The next prime is 21533431. The reversal of 21533421 is 12433512.

It is not a de Polignac number, because 21533421 - 2⁶ = 21533357 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21533431) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 39166 + ... + 39711.

It is an arithmetic number, because the mean of its divisors is an integer number (2208584).

Almost surely, 2^21533421 is an apocalyptic number.

21533421 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21533421 is a deficient number, since it is larger than the sum of its proper divisors (13803923).

21533421 is a wasteful number, since it uses less digits than its factorization.

21533421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 78900.

The product of its digits is 720, while the sum is 21.

The square root of 21533421 is about 4640.4117274225. The cubic root of 21533421 is about 278.2088944573.

Adding to 21533421 its reverse (12433512), we get a palindrome (33966933).

Subtracting from 21533421 its reverse (12433512), we obtain a palindrome (9099909).

The spelling of 21533421 in words is "twenty-one million, five hundred thirty-three thousand, four hundred twenty-one".