1666991 has 2 divisors, whose sum is σ = 1666992. Its totient is φ = 1666990.

The previous prime is 1666943. The next prime is 1666999. The reversal of 1666991 is 1996661.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 1666991 - 2¹⁰ = 1665967 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1666999) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 833495 + 833496.

It is an arithmetic number, because the mean of its divisors is an integer number (833496).

2^1666991 is an apocalyptic number.

1666991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1666991 is an equidigital number, since it uses as much as digits as its factorization.

1666991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 17496, while the sum is 38.

The square root of 1666991 is about 1291.1200563852. The cubic root of 1666991 is about 118.5708004446.

The spelling of 1666991 in words is "one million, six hundred sixty-six thousand, nine hundred ninety-one".