19999981 has 2 divisors, whose sum is σ = 19999982.
Its totient is φ = 19999980.
The previous prime is 19999963. The next prime is 19999999. The reversal of 19999981 is 18999991.
It can be divided in two parts, 19 and 999981, that added together give a 6-th power (1000000 = 106).
It is a balanced prime because it is at equal distance from previous prime (19999963) and next prime (19999999).
It can be written as a sum of positive squares in only one way, i.e., 14402025 + 5597956 = 3795^2 + 2366^2
It is an emirp because it is prime and its reverse (18999991) is a distict prime.
It is a cyclic number.
It is not a de Polignac number, because 19999981 - 213 = 19991789 is a prime.
It is a super-2 number, since 2×199999812 = 799998480000722, which contains 22 as substring.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (19999481) by changing a digit.
It is a pernicious number, because its binary representation contains a prime number (13) of ones.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9999990 + 9999991.
It is an arithmetic number, because the mean of its divisors is an integer number (9999991).
Almost surely, 219999981 is an apocalyptic number.
It is an amenable number.
19999981 is a deficient number, since it is larger than the sum of its proper divisors (1).
19999981 is an equidigital number, since it uses as much as digits as its factorization.
19999981 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 472392, while the sum is 55.
The square root of 19999981 is about 4472.1338307345.
The cubic root of 19999981 is about 271.4416757029.
The spelling of 19999981 in words is "nineteen million, nine hundred ninety-nine thousand, nine hundred eighty-one".