21215255 has 4 divisors (see below), whose sum is σ = 25458312. Its totient is φ = 16972200.

The previous prime is 21215237. The next prime is 21215261. The reversal of 21215255 is 55251212.

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

It is not a de Polignac number, because 21215255 - 2¹⁰ = 21214231 is a prime.

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 21215255.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2121521 + ... + 2121530.

It is an arithmetic number, because the mean of its divisors is an integer number (6364578).

Almost surely, 2^21215255 is an apocalyptic number.

21215255 is a deficient number, since it is larger than the sum of its proper divisors (4243057).

21215255 is an equidigital number, since it uses as much as digits as its factorization.

21215255 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4243056.

The product of its digits is 1000, while the sum is 23.

The square root of 21215255 is about 4606.0020625267. The cubic root of 21215255 is about 276.8318693676.

Adding to 21215255 its reverse (55251212), we get a palindrome (76466467).

The spelling of 21215255 in words is "twenty-one million, two hundred fifteen thousand, two hundred fifty-five".