1991641 has 2 divisors, whose sum is σ = 1991642. Its totient is φ = 1991640.

The previous prime is 1991623. The next prime is 1991653. The reversal of 1991641 is 1461991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1901641 + 90000 = 1379^2 + 300^2 .

It is a cyclic number.

It is not a de Polignac number, because 1991641 - 2⁵ = 1991609 is a prime.

It is a Chen prime.

1991641 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (1991681) 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, 995820 + 995821.

It is an arithmetic number, because the mean of its divisors is an integer number (995821).

2^1991641 is an apocalyptic number.

It is an amenable number.

1991641 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991641 is an equidigital number, since it uses as much as digits as its factorization.

1991641 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1944, while the sum is 31.

The square root of 1991641 is about 1411.2551151369. The cubic root of 1991641 is about 125.8163318794.

The spelling of 1991641 in words is "one million, nine hundred ninety-one thousand, six hundred forty-one".