21281712817 has 2 divisors, whose sum is σ = 21281712818. Its totient is φ = 21281712816.

The previous prime is 21281712811. The next prime is 21281712821. The reversal of 21281712817 is 71821718212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13939108096 + 7342604721 = 118064^2 + 85689^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21281712817 is a prime.

It is a super-2 number, since 2×21281712817² (a number of 21 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21281712817.

It is not a weakly prime, because it can be changed into another prime (21281712811) 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 as a sum of consecutive naturals, namely, 10640856408 + 10640856409.

It is an arithmetic number, because the mean of its divisors is an integer number (10640856409).

Almost surely, 2^21281712817 is an apocalyptic number.

It is an amenable number.

21281712817 is a deficient number, since it is larger than the sum of its proper divisors (1).

21281712817 is an equidigital number, since it uses as much as digits as its factorization.

21281712817 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 25088, while the sum is 40.

The spelling of 21281712817 in words is "twenty-one billion, two hundred eighty-one million, seven hundred twelve thousand, eight hundred seventeen".