21213255 has 16 divisors (see below), whose sum is σ = 38790144. Its totient is φ = 9697440.

The previous prime is 21213251. The next prime is 21213287. The reversal of 21213255 is 55231212.

It is not a de Polignac number, because 21213255 - 2² = 21213251 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 (21213251) 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 15 ways as a sum of consecutive naturals, for example, 100911 + ... + 101120.

It is an arithmetic number, because the mean of its divisors is an integer number (2424384).

Almost surely, 2^21213255 is an apocalyptic number.

21213255 is a deficient number, since it is larger than the sum of its proper divisors (17576889).

21213255 is a wasteful number, since it uses less digits than its factorization.

21213255 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 202046.

The product of its digits is 600, while the sum is 21.

The square root of 21213255 is about 4605.7849493870. The cubic root of 21213255 is about 276.8231699492.

Adding to 21213255 its reverse (55231212), we get a palindrome (76444467).

The spelling of 21213255 in words is "twenty-one million, two hundred thirteen thousand, two hundred fifty-five".