21212351 has 4 divisors (see below), whose sum is σ = 21226032. Its totient is φ = 21198672.

The previous prime is 21212297. The next prime is 21212353. The reversal of 21212351 is 15321212.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21212351 - 2²² = 17018047 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21212353) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4166 + ... + 7731.

It is an arithmetic number, because the mean of its divisors is an integer number (5306508).

Almost surely, 2^21212351 is an apocalyptic number.

21212351 is a deficient number, since it is larger than the sum of its proper divisors (13681).

21212351 is a wasteful number, since it uses less digits than its factorization.

21212351 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13680.

The product of its digits is 120, while the sum is 17.

The square root of 21212351 is about 4605.6868108893. The cubic root of 21212351 is about 276.8192376327.

Adding to 21212351 its reverse (15321212), we get a palindrome (36533563).

The spelling of 21212351 in words is "twenty-one million, two hundred twelve thousand, three hundred fifty-one".