19918081 has 2 divisors, whose sum is σ = 19918082. Its totient is φ = 19918080.

The previous prime is 19918057. The next prime is 19918097. The reversal of 19918081 is 18081991.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14554225 + 5363856 = 3815^2 + 2316^2 .

It is an emirp because it is prime and its reverse (18081991) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 19918081 - 2⁵ = 19918049 is a prime.

It is a super-2 number, since 2×19918081² = 793459901445122, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 19918081.

It is not a weakly prime, because it can be changed into another prime (19918001) 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, 9959040 + 9959041.

It is an arithmetic number, because the mean of its divisors is an integer number (9959041).

Almost surely, 2^19918081 is an apocalyptic number.

It is an amenable number.

19918081 is a deficient number, since it is larger than the sum of its proper divisors (1).

19918081 is an equidigital number, since it uses as much as digits as its factorization.

19918081 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5184, while the sum is 37.

The square root of 19918081 is about 4462.9677345910. The cubic root of 19918081 is about 271.0706505520.

The spelling of 19918081 in words is "nineteen million, nine hundred eighteen thousand, eighty-one".