199999999981 has 4 divisors (see below), whose sum is σ = 200078649792. Its totient is φ = 199921350172.

The previous prime is 199999999949. The next prime is 200000000041. The reversal of 199999999981 is 189999999991.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 189999999991 = 274177 ⋅692983.

It is a cyclic number.

It is not a de Polignac number, because 199999999981 - 2⁵ = 199999999949 is a prime.

It is a super-2 number, since 2×199999999981² (a number of 23 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (199999999921) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 39321091 + ... + 39326176.

It is an arithmetic number, because the mean of its divisors is an integer number (50019662448).

Almost surely, 2^199999999981 is an apocalyptic number.

It is an amenable number.

199999999981 is a deficient number, since it is larger than the sum of its proper divisors (78649811).

199999999981 is an equidigital number, since it uses as much as digits as its factorization.

199999999981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 78649810.

The product of its digits is 3099363912, while the sum is 91.

It can be divided in two parts, 19 and 9999999981, that added together give a 10-th power (10000000000 = 10¹⁰).

The spelling of 199999999981 in words is "one hundred ninety-nine billion, nine hundred ninety-nine million, nine hundred ninety-nine thousand, nine hundred eighty-one".