999997999981 has 2 divisors, whose sum is σ = 999997999982. Its totient is φ = 999997999980.

The previous prime is 999997999919. The next prime is 999998000009. The reversal of 999997999981 is 189999799999.

999997999981 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 971821356100 + 28176643881 = 985810^2 + 167859^2 .

It is an emirp because it is prime and its reverse (189999799999) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 999997999981 - 2²³ = 999989611373 is a prime.

It is a super-2 number, since 2×999997999981² (a number of 25 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (999997999681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499998999990 + 499998999991.

It is an arithmetic number, because the mean of its divisors is an integer number (499998999991).

Almost surely, 2^999997999981 is an apocalyptic number.

It is an amenable number.

999997999981 is a deficient number, since it is larger than the sum of its proper divisors (1).

999997999981 is an equidigital number, since it uses as much as digits as its factorization.

999997999981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 21695547384, while the sum is 97.

It can be divided in two parts, 99999799998 and 1, that added together give a palindrome (99999799999).

The spelling of 999997999981 in words is "nine hundred ninety-nine billion, nine hundred ninety-seven million, nine hundred ninety-nine thousand, nine hundred eighty-one".