21085284917 has 2 divisors, whose sum is σ = 21085284918. Its totient is φ = 21085284916.

The previous prime is 21085284851. The next prime is 21085284919. The reversal of 21085284917 is 71948258012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21073167556 + 12117361 = 145166^2 + 3481^2 .

It is a cyclic number.

It is not a de Polignac number, because 21085284917 - 2¹⁰ = 21085283893 is a prime.

Together with 21085284919, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21085284919) 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, 10542642458 + 10542642459.

It is an arithmetic number, because the mean of its divisors is an integer number (10542642459).

Almost surely, 2^21085284917 is an apocalyptic number.

It is an amenable number.

21085284917 is a deficient number, since it is larger than the sum of its proper divisors (1).

21085284917 is an equidigital number, since it uses as much as digits as its factorization.

21085284917 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 322560, while the sum is 47.

The spelling of 21085284917 in words is "twenty-one billion, eighty-five million, two hundred eighty-four thousand, nine hundred seventeen".