21005011715 has 4 divisors (see below), whose sum is σ = 25206014064. Its totient is φ = 16804009368.

The previous prime is 21005011693. The next prime is 21005011771. The reversal of 21005011715 is 51711050012.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21005011715 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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, 2100501167 + ... + 2100501176.

It is an arithmetic number, because the mean of its divisors is an integer number (6301503516).

Almost surely, 2^21005011715 is an apocalyptic number.

21005011715 is a deficient number, since it is larger than the sum of its proper divisors (4201002349).

21005011715 is an equidigital number, since it uses as much as digits as its factorization.

21005011715 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4201002348.

The product of its (nonzero) digits is 350, while the sum is 23.

Adding to 21005011715 its reverse (51711050012), we get a palindrome (72716061727).

The spelling of 21005011715 in words is "twenty-one billion, five million, eleven thousand, seven hundred fifteen".