1666391549 has 2 divisors, whose sum is σ = 1666391550. Its totient is φ = 1666391548.

The previous prime is 1666391537. The next prime is 1666391593. The reversal of 1666391549 is 9451936661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1482789049 + 183602500 = 38507^2 + 13550^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1666391549 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 1666391497 and 1666391506.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1666391509) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 833195774 + 833195775.

It is an arithmetic number, because the mean of its divisors is an integer number (833195775).

Almost surely, 2^1666391549 is an apocalyptic number.

It is an amenable number.

1666391549 is a deficient number, since it is larger than the sum of its proper divisors (1).

1666391549 is an equidigital number, since it uses as much as digits as its factorization.

1666391549 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1049760, while the sum is 50.

The square root of 1666391549 is about 40821.4594178111. The cubic root of 1666391549 is about 1185.5658602943.

The spelling of 1666391549 in words is "one billion, six hundred sixty-six million, three hundred ninety-one thousand, five hundred forty-nine".