21212321 has 8 divisors (see below), whose sum is σ = 22926120. Its totient is φ = 19510272.

The previous prime is 21212297. The next prime is 21212353. The reversal of 21212321 is 12321212.

It is a happy number.

21212321 is an esthetic number in base 10, because in such base its adjacent digits differ by 1.

It can be written as a sum of positive squares in 4 ways, for example, as 1852321 + 19360000 = 1361^2 + 4400^2 .

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 21212321 - 2²² = 17018017 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21212296 and 21212305.

It is not an unprimeable number, because it can be changed into a prime (21214321) 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 7 ways as a sum of consecutive naturals, for example, 1025 + ... + 6593.

It is an arithmetic number, because the mean of its divisors is an integer number (2865765).

Almost surely, 2^21212321 is an apocalyptic number.

It is an amenable number.

21212321 is a deficient number, since it is larger than the sum of its proper divisors (1713799).

21212321 is a wasteful number, since it uses less digits than its factorization.

21212321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5875.

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

The square root of 21212321 is about 4605.6835540449. The cubic root of 21212321 is about 276.8191071335.

Adding to 21212321 its reverse (12321212), we get a palindrome (33533533).

The spelling of 21212321 in words is "twenty-one million, two hundred twelve thousand, three hundred twenty-one".