999998566681021 has 2 divisors, whose sum is σ = 999998566681022. Its totient is φ = 999998566681020.

The previous prime is 999998566680913. The next prime is 999998566681069. The reversal of 999998566681021 is 120186665899999.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 952564891322500 + 47433675358521 = 30863650^2 + 6887211^2 .

It is an emirp because it is prime and its reverse (120186665899999) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 999998566681021 - 2²⁷ = 999998432463293 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (999998566681321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499999283340510 + 499999283340511.

It is an arithmetic number, because the mean of its divisors is an integer number (499999283340511).

Almost surely, 2^{999998566681021} is an apocalyptic number.

It is an amenable number.

999998566681021 is a deficient number, since it is larger than the sum of its proper divisors (1).

999998566681021 is an equidigital number, since it uses as much as digits as its factorization.

999998566681021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 8162933760, while the sum is 88.

The spelling of 999998566681021 in words is "nine hundred ninety-nine trillion, nine hundred ninety-eight billion, five hundred sixty-six million, six hundred eighty-one thousand, twenty-one".