1813991 has 2 divisors, whose sum is σ = 1813992. Its totient is φ = 1813990.

The previous prime is 1813969. The next prime is 1813993. The reversal of 1813991 is 1993181.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1813991 is a prime.

Together with 1813993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1813993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 906995 + 906996.

It is an arithmetic number, because the mean of its divisors is an integer number (906996).

2^1813991 is an apocalyptic number.

1813991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1813991 is an equidigital number, since it uses as much as digits as its factorization.

1813991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1944, while the sum is 32.

The square root of 1813991 is about 1346.8448314487. The cubic root of 1813991 is about 121.9583975323.

The spelling of 1813991 in words is "one million, eight hundred thirteen thousand, nine hundred ninety-one".