1643891 has 2 divisors, whose sum is σ = 1643892. Its totient is φ = 1643890.

The previous prime is 1643881. The next prime is 1643893. The reversal of 1643891 is 1983461.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 1643891 - 2⁶ = 1643827 is a prime.

Together with 1643893, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (1643893) 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, 821945 + 821946.

It is an arithmetic number, because the mean of its divisors is an integer number (821946).

2^1643891 is an apocalyptic number.

1643891 is a deficient number, since it is larger than the sum of its proper divisors (1).

1643891 is an equidigital number, since it uses as much as digits as its factorization.

1643891 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5184, while the sum is 32.

The square root of 1643891 is about 1282.1431277357. The cubic root of 1643891 is about 118.0205604315.

The spelling of 1643891 in words is "one million, six hundred forty-three thousand, eight hundred ninety-one".