1721868821 has 2 divisors, whose sum is σ = 1721868822. Its totient is φ = 1721868820.

The previous prime is 1721868773. The next prime is 1721868839. The reversal of 1721868821 is 1288681271.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1575216721 + 146652100 = 39689^2 + 12110^2 .

It is an emirp because it is prime and its reverse (1288681271) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1721868821 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1721868721) 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, 860934410 + 860934411.

It is an arithmetic number, because the mean of its divisors is an integer number (860934411).

Almost surely, 2^1721868821 is an apocalyptic number.

It is an amenable number.

1721868821 is a deficient number, since it is larger than the sum of its proper divisors (1).

1721868821 is an equidigital number, since it uses as much as digits as its factorization.

1721868821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 86016, while the sum is 44.

The square root of 1721868821 is about 41495.4072277885. The cubic root of 1721868821 is about 1198.5790637160.

The spelling of 1721868821 in words is "one billion, seven hundred twenty-one million, eight hundred sixty-eight thousand, eight hundred twenty-one".