21221213 has 8 divisors (see below), whose sum is σ = 22909656. Its totient is φ = 19540800.

The previous prime is 21221171. The next prime is 21221237. The reversal of 21221213 is 31212212.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 88804 + 21132409 = 298^2 + 4597^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21221213 - 2¹² = 21217117 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21221273) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4223 + ... + 7763.

It is an arithmetic number, because the mean of its divisors is an integer number (2863707).

Almost surely, 2^21221213 is an apocalyptic number.

It is an amenable number.

21221213 is a deficient number, since it is larger than the sum of its proper divisors (1688443).

21221213 is a wasteful number, since it uses less digits than its factorization.

21221213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4015.

The product of its digits is 48, while the sum is 14.

The square root of 21221213 is about 4606.6487819238. The cubic root of 21221213 is about 276.8577816950.

Adding to 21221213 its reverse (31212212), we get a palindrome (52433425).

Subtracting 21221213 from its reverse (31212212), we obtain a palindrome (9990999).

The spelling of 21221213 in words is "twenty-one million, two hundred twenty-one thousand, two hundred thirteen".