21109993717 has 2 divisors, whose sum is σ = 21109993718. Its totient is φ = 21109993716.

The previous prime is 21109993669. The next prime is 21109993753. The reversal of 21109993717 is 71739990112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20371567441 + 738426276 = 142729^2 + 27174^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21109993717 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21109993787) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10554996858 + 10554996859.

It is an arithmetic number, because the mean of its divisors is an integer number (10554996859).

Almost surely, 2^21109993717 is an apocalyptic number.

It is an amenable number.

21109993717 is a deficient number, since it is larger than the sum of its proper divisors (1).

21109993717 is an equidigital number, since it uses as much as digits as its factorization.

21109993717 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 214326, while the sum is 49.

The spelling of 21109993717 in words is "twenty-one billion, one hundred nine million, nine hundred ninety-three thousand, seven hundred seventeen".