18991081 has 2 divisors, whose sum is σ = 18991082. Its totient is φ = 18991080.

The previous prime is 18991067. The next prime is 18991117. The reversal of 18991081 is 18019981.

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., 15531481 + 3459600 = 3941^2 + 1860^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18991081 is a prime.

It is a super-2 number, since 2×18991081² = 721322315097122, 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 18991081.

It is not a weakly prime, because it can be changed into another prime (18991001) 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, 9495540 + 9495541.

It is an arithmetic number, because the mean of its divisors is an integer number (9495541).

Almost surely, 2^18991081 is an apocalyptic number.

It is an amenable number.

18991081 is a deficient number, since it is larger than the sum of its proper divisors (1).

18991081 is an equidigital number, since it uses as much as digits as its factorization.

18991081 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 18991081 is about 4357.8757439835. The cubic root of 18991081 is about 266.7984048735.

The spelling of 18991081 in words is "eighteen million, nine hundred ninety-one thousand, eighty-one".