21021816 has 32 divisors (see below), whose sum is σ = 54840960. Its totient is φ = 6702432.

The previous prime is 21021799. The next prime is 21021823. The reversal of 21021816 is 61812012.

It is a junction number, because it is equal to n+sod(n) for n = 21021792 and 21021801.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 18490 + ... + 19593.

It is an arithmetic number, because the mean of its divisors is an integer number (1713780).

Almost surely, 2^21021816 is an apocalyptic number.

It is an amenable number.

21021816 is an abundant number, since it is smaller than the sum of its proper divisors (33819144).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21021816 is a wasteful number, since it uses less digits than its factorization.

21021816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 38115 (or 38111 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 21.

The square root of 21021816 is about 4584.9553978201. The cubic root of 21021816 is about 275.9879221768.

Adding to 21021816 its reverse (61812012), we get a palindrome (82833828).

The spelling of 21021816 in words is "twenty-one million, twenty-one thousand, eight hundred sixteen".