21156211717 has 2 divisors, whose sum is σ = 21156211718. Its totient is φ = 21156211716.

The previous prime is 21156211691. The next prime is 21156211753. The reversal of 21156211717 is 71711265112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17352529441 + 3803682276 = 131729^2 + 61674^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21156211717 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21156211757) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10578105858 + 10578105859.

It is an arithmetic number, because the mean of its divisors is an integer number (10578105859).

Almost surely, 2^21156211717 is an apocalyptic number.

It is an amenable number.

21156211717 is a deficient number, since it is larger than the sum of its proper divisors (1).

21156211717 is an equidigital number, since it uses as much as digits as its factorization.

21156211717 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5880, while the sum is 34.

Adding to 21156211717 its reverse (71711265112), we get a palindrome (92867476829).

The spelling of 21156211717 in words is "twenty-one billion, one hundred fifty-six million, two hundred eleven thousand, seven hundred seventeen".