18991969 has 2 divisors, whose sum is σ = 18991970. Its totient is φ = 18991968.

The previous prime is 18991949. The next prime is 18991981. The reversal of 18991969 is 96919981.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 9610000 + 9381969 = 3100^2 + 3063^2 .

It is a cyclic number.

It is not a de Polignac number, because 18991969 - 2⁵ = 18991937 is a prime.

It is a super-2 number, since 2×18991969² = 721389772993922, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (18991909) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9495984 + 9495985.

It is an arithmetic number, because the mean of its divisors is an integer number (9495985).

Almost surely, 2^18991969 is an apocalyptic number.

It is an amenable number.

18991969 is a deficient number, since it is larger than the sum of its proper divisors (1).

18991969 is an equidigital number, since it uses as much as digits as its factorization.

18991969 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 314928, while the sum is 52.

The square root of 18991969 is about 4357.9776272946. The cubic root of 18991969 is about 266.8025631990.

The spelling of 18991969 in words is "eighteen million, nine hundred ninety-one thousand, nine hundred sixty-nine".