21311756815 has 4 divisors (see below), whose sum is σ = 25574108184. Its totient is φ = 17049405448.

The previous prime is 21311756813. The next prime is 21311756821. The reversal of 21311756815 is 51865711312.

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

It is a cyclic number.

It is not a de Polignac number, because 21311756815 - 2¹ = 21311756813 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 a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21311756813) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2131175677 + ... + 2131175686.

It is an arithmetic number, because the mean of its divisors is an integer number (6393527046).

Almost surely, 2^21311756815 is an apocalyptic number.

21311756815 is a deficient number, since it is larger than the sum of its proper divisors (4262351369).

21311756815 is an equidigital number, since it uses as much as digits as its factorization.

21311756815 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4262351368.

The product of its digits is 50400, while the sum is 40.

The spelling of 21311756815 in words is "twenty-one billion, three hundred eleven million, seven hundred fifty-six thousand, eight hundred fifteen".