21105816 has 64 divisors (see below), whose sum is σ = 54885600. Its totient is φ = 6758400.

The previous prime is 21105811. The next prime is 21105863. The reversal of 21105816 is 61850112.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21105811) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 87456 + ... + 87696.

Almost surely, 2^21105816 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21105816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27442800).

21105816 is an abundant number, since it is smaller than the sum of its proper divisors (33779784).

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

21105816 is a wasteful number, since it uses less digits than its factorization.

21105816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 380 (or 376 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 24.

The square root of 21105816 is about 4594.1066596238. The cubic root of 21105816 is about 276.3550356437.

Adding to 21105816 its reverse (61850112), we get a palindrome (82955928).

The spelling of 21105816 in words is "twenty-one million, one hundred five thousand, eight hundred sixteen".