21105810 has 48 divisors (see below), whose sum is σ = 59866560. Its totient is φ = 5116320.

The previous prime is 21105781. The next prime is 21105811. The reversal of 21105810 is 1850112.

It is a super-2 number, since 2×21105810² = 890910431512200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (18).

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 23 ways as a sum of consecutive naturals, for example, 9670 + ... + 11649.

It is an arithmetic number, because the mean of its divisors is an integer number (1247220).

Almost surely, 2^21105810 is an apocalyptic number.

21105810 is an abundant number, since it is smaller than the sum of its proper divisors (38760750).

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

21105810 is a wasteful number, since it uses less digits than its factorization.

21105810 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21343 (or 21340 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 18.

The square root of 21105810 is about 4594.1060066133. The cubic root of 21105810 is about 276.3550094562.

Adding to 21105810 its reverse (1850112), we get a palindrome (22955922).

The spelling of 21105810 in words is "twenty-one million, one hundred five thousand, eight hundred ten".