1644991 has 2 divisors, whose sum is σ = 1644992. Its totient is φ = 1644990.

The previous prime is 1644989. The next prime is 1644997. The reversal of 1644991 is 1994461.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1644991 - 2¹ = 1644989 is a prime.

Together with 1644989, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1644997) 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, 822495 + 822496.

It is an arithmetic number, because the mean of its divisors is an integer number (822496).

2^1644991 is an apocalyptic number.

1644991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1644991 is an equidigital number, since it uses as much as digits as its factorization.

1644991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7776, while the sum is 34.

The square root of 1644991 is about 1282.5720252680. The cubic root of 1644991 is about 118.0468788169.

The spelling of 1644991 in words is "one million, six hundred forty-four thousand, nine hundred ninety-one".