21121085717 has 2 divisors, whose sum is σ = 21121085718. Its totient is φ = 21121085716.

The previous prime is 21121085681. The next prime is 21121085731. The reversal of 21121085717 is 71758012112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21103663441 + 17422276 = 145271^2 + 4174^2 .

It is a cyclic number.

It is not a de Polignac number, because 21121085717 - 2¹⁰ = 21121084693 is a prime.

It is a super-2 number, since 2×21121085717² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21121085317) 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, 10560542858 + 10560542859.

It is an arithmetic number, because the mean of its divisors is an integer number (10560542859).

Almost surely, 2^21121085717 is an apocalyptic number.

It is an amenable number.

21121085717 is a deficient number, since it is larger than the sum of its proper divisors (1).

21121085717 is an equidigital number, since it uses as much as digits as its factorization.

21121085717 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 7840, while the sum is 35.

Adding to 21121085717 its reverse (71758012112), we get a palindrome (92879097829).

The spelling of 21121085717 in words is "twenty-one billion, one hundred twenty-one million, eighty-five thousand, seven hundred seventeen".