21006812 has 12 divisors (see below), whose sum is σ = 36797040. Its totient is φ = 10493376.

The previous prime is 21006803. The next prime is 21006829. The reversal of 21006812 is 21860012.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4193 + ... + 7719.

It is an arithmetic number, because the mean of its divisors is an integer number (3066420).

Almost surely, 2^21006812 is an apocalyptic number.

It is an amenable number.

21006812 is a deficient number, since it is larger than the sum of its proper divisors (15790228).

21006812 is a wasteful number, since it uses less digits than its factorization.

21006812 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5020 (or 5018 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 20.

The square root of 21006812 is about 4583.3188848257. The cubic root of 21006812 is about 275.9222458282.

Adding to 21006812 its reverse (21860012), we get a palindrome (42866824).

The spelling of 21006812 in words is "twenty-one million, six thousand, eight hundred twelve".