1991819 has 2 divisors, whose sum is σ = 1991820. Its totient is φ = 1991818.

The previous prime is 1991797. The next prime is 1991837. The reversal of 1991819 is 9181991.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 1991819 - 2¹⁶ = 1926283 is a prime.

It is a super-2 number, since 2×1991819² = 7934685857522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (1991849) 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, 995909 + 995910.

It is an arithmetic number, because the mean of its divisors is an integer number (995910).

2^1991819 is an apocalyptic number.

1991819 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991819 is an equidigital number, since it uses as much as digits as its factorization.

1991819 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5832, while the sum is 38.

The square root of 1991819 is about 1411.3181781583. The cubic root of 1991819 is about 125.8200799846.

The spelling of 1991819 in words is "one million, nine hundred ninety-one thousand, eight hundred nineteen".