1981891 has 2 divisors, whose sum is σ = 1981892. Its totient is φ = 1981890.

The previous prime is 1981883. The next prime is 1981901.

It is a happy number.

1981891 is nontrivially palindromic in base 10.

It is a weak prime.

It is a palprime.

It is a cyclic number.

It is not a de Polignac number, because 1981891 - 2³ = 1981883 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1981891.

It is not a weakly prime, because it can be changed into another prime (1981691) 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, 990945 + 990946.

It is an arithmetic number, because the mean of its divisors is an integer number (990946).

2^1981891 is an apocalyptic number.

1981891 is a deficient number, since it is larger than the sum of its proper divisors (1).

1981891 is an equidigital number, since it uses as much as digits as its factorization.

1981891 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5184, while the sum is 37.

The square root of 1981891 is about 1407.7965051811. The cubic root of 1981891 is about 125.6106863059.

The spelling of 1981891 in words is "one million, nine hundred eighty-one thousand, eight hundred ninety-one".