21216812 has 6 divisors (see below), whose sum is σ = 37129428. Its totient is φ = 10608404.

The previous prime is 21216809. The next prime is 21216827. The reversal of 21216812 is 21861212.

It is a super-2 number, since 2×21216812² = 900306222886688, which contains 22 as substring.

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 2652098 + ... + 2652105.

It is an arithmetic number, because the mean of its divisors is an integer number (6188238).

Almost surely, 2^21216812 is an apocalyptic number.

It is an amenable number.

21216812 is a deficient number, since it is larger than the sum of its proper divisors (15912616).

21216812 is a wasteful number, since it uses less digits than its factorization.

21216812 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5304207 (or 5304205 counting only the distinct ones).

The product of its digits is 384, while the sum is 23.

The square root of 21216812 is about 4606.1710780213. The cubic root of 21216812 is about 276.8386414863.

The spelling of 21216812 in words is "twenty-one million, two hundred sixteen thousand, eight hundred twelve".