1999999999981 has 2 divisors, whose sum is σ = 1999999999982. Its totient is φ = 1999999999980.

The previous prime is 1999999999927. The next prime is 2000000000003. The reversal of 1999999999981 is 1899999999991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1416716487081 + 583283512900 = 1190259^2 + 763730^2 .

It is a cyclic number.

It is not a de Polignac number, because 1999999999981 - 2¹³ = 1999999991789 is a prime.

It is a super-2 number, since 2×1999999999981² (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 (1999999999901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 999999999990 + 999999999991.

It is an arithmetic number, because the mean of its divisors is an integer number (999999999991).

Almost surely, 2^{1999999999981} is an apocalyptic number.

It is an amenable number.

1999999999981 is a deficient number, since it is larger than the sum of its proper divisors (1).

1999999999981 is an equidigital number, since it uses as much as digits as its factorization.

1999999999981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 27894275208, while the sum is 100.

It can be divided in two parts, 19 and 99999999981, that added together give a 11-th power (100000000000 = 10¹¹).

The spelling of 1999999999981 in words is "one trillion, nine hundred ninety-nine billion, nine hundred ninety-nine million, nine hundred ninety-nine thousand, nine hundred eighty-one".