199961818981 has 2 divisors, whose sum is σ = 199961818982. Its totient is φ = 199961818980.

The previous prime is 199961818957. The next prime is 199961819033. The reversal of 199961818981 is 189818169991.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 199928813956 + 33005025 = 447134^2 + 5745^2 .

It is an emirp because it is prime and its reverse (189818169991) is a distict prime. It is also a bemirp because it and its reverse can be mirrored producing other two distinct primes, 186818196661 and 166691818681.

It is a cyclic number.

It is not a de Polignac number, because 199961818981 - 2¹⁹ = 199961294693 is a prime.

It is a super-2 number, since 2×199961818981² (a number of 23 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 199961818981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (199961818681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 99980909490 + 99980909491.

It is an arithmetic number, because the mean of its divisors is an integer number (99980909491).

Almost surely, 2^199961818981 is an apocalyptic number.

It is an amenable number.

199961818981 is a deficient number, since it is larger than the sum of its proper divisors (1).

199961818981 is an equidigital number, since it uses as much as digits as its factorization.

199961818981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20155392, while the sum is 70.

The spelling of 199961818981 in words is "one hundred ninety-nine billion, nine hundred sixty-one million, eight hundred eighteen thousand, nine hundred eighty-one".