1668039721 has 2 divisors, whose sum is σ = 1668039722. Its totient is φ = 1668039720.

The previous prime is 1668039713. The next prime is 1668039731. The reversal of 1668039721 is 1279308661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1444836121 + 223203600 = 38011^2 + 14940^2 .

It is an emirp because it is prime and its reverse (1279308661) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1668039721 - 2³ = 1668039713 is a prime.

It is not a weakly prime, because it can be changed into another prime (1668039731) 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, 834019860 + 834019861.

It is an arithmetic number, because the mean of its divisors is an integer number (834019861).

Almost surely, 2^1668039721 is an apocalyptic number.

It is an amenable number.

1668039721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1668039721 is an equidigital number, since it uses as much as digits as its factorization.

1668039721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 108864, while the sum is 43.

The square root of 1668039721 is about 40841.6419968639. The cubic root of 1668039721 is about 1185.9565993121.

The spelling of 1668039721 in words is "one billion, six hundred sixty-eight million, thirty-nine thousand, seven hundred twenty-one".