21105865 has 24 divisors (see below), whose sum is σ = 29187648. Its totient is φ = 14528160.

The previous prime is 21105863. The next prime is 21105907. The reversal of 21105865 is 56850112.

It is not a de Polignac number, because 21105865 - 2¹ = 21105863 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21105863) 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, 19324 + ... + 20386.

It is an arithmetic number, because the mean of its divisors is an integer number (1216152).

Almost surely, 2^21105865 is an apocalyptic number.

It is an amenable number.

21105865 is a deficient number, since it is larger than the sum of its proper divisors (8081783).

21105865 is a wasteful number, since it uses less digits than its factorization.

21105865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1117 (or 1098 counting only the distinct ones).

The product of its (nonzero) digits is 2400, while the sum is 28.

The square root of 21105865 is about 4594.1119925400. Note that the first 3 decimals coincide. The cubic root of 21105865 is about 276.3552495087.

Adding to 21105865 its reverse (56850112), we get a palindrome (77955977).

The spelling of 21105865 in words is "twenty-one million, one hundred five thousand, eight hundred sixty-five".