21621213 has 12 divisors (see below), whose sum is σ = 31659420. Its totient is φ = 14216256.

The previous prime is 21621181. The next prime is 21621233. The reversal of 21621213 is 31212612.

21621213 is a `hidden beast` number, since 21 + 621 + 21 + 3 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 15657849 + 5963364 = 3957^2 + 2442^2 .

It is not a de Polignac number, because 21621213 - 2⁵ = 21621181 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21621233) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 15798 + ... + 17111.

It is an arithmetic number, because the mean of its divisors is an integer number (2638285).

Almost surely, 2^21621213 is an apocalyptic number.

It is an amenable number.

21621213 is a deficient number, since it is larger than the sum of its proper divisors (10038207).

21621213 is a wasteful number, since it uses less digits than its factorization.

21621213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32988 (or 32985 counting only the distinct ones).

The product of its digits is 144, while the sum is 18.

The square root of 21621213 is about 4649.8616108439. The cubic root of 21621213 is about 278.5864687287.

Adding to 21621213 its reverse (31212612), we get a palindrome (52833825).

It can be divided in two parts, 216212 and 13, that added together give a square (216225 = 465²).

The spelling of 21621213 in words is "twenty-one million, six hundred twenty-one thousand, two hundred thirteen".