21212747 has 4 divisors (see below), whose sum is σ = 21418800. Its totient is φ = 21006696.

The previous prime is 21212731. The next prime is 21212749. The reversal of 21212747 is 74721212.

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 21212747 - 2⁴ = 21212731 is a prime.

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

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21212749) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 102872 + ... + 103077.

It is an arithmetic number, because the mean of its divisors is an integer number (5354700).

Almost surely, 2^21212747 is an apocalyptic number.

21212747 is a deficient number, since it is larger than the sum of its proper divisors (206053).

21212747 is a wasteful number, since it uses less digits than its factorization.

21212747 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 206052.

The product of its digits is 1568, while the sum is 26.

The square root of 21212747 is about 4605.7298010196. The cubic root of 21212747 is about 276.8209602099.

Adding to 21212747 its reverse (74721212), we get a palindrome (95933959).

The spelling of 21212747 in words is "twenty-one million, two hundred twelve thousand, seven hundred forty-seven".