21101853865 has 4 divisors (see below), whose sum is σ = 25322224644. Its totient is φ = 16881483088.

The previous prime is 21101853859. The next prime is 21101853893. The reversal of 21101853865 is 56835810112.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 12161016729 + 8940837136 = 110277^2 + 94556^2 .

It is a cyclic number.

It is not a de Polignac number, because 21101853865 - 2⁵ = 21101853833 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian 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, 2110185382 + ... + 2110185391.

It is an arithmetic number, because the mean of its divisors is an integer number (6330556161).

Almost surely, 2^21101853865 is an apocalyptic number.

It is an amenable number.

21101853865 is a deficient number, since it is larger than the sum of its proper divisors (4220370779).

21101853865 is an equidigital number, since it uses as much as digits as its factorization.

21101853865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4220370778.

The product of its (nonzero) digits is 57600, while the sum is 40.

The spelling of 21101853865 in words is "twenty-one billion, one hundred one million, eight hundred fifty-three thousand, eight hundred sixty-five".