6721868557 has 4 divisors (see below), whose sum is σ = 6797395260. Its totient is φ = 6646341856.

The previous prime is 6721868537. The next prime is 6721868609. The reversal of 6721868557 is 7558681276.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 877877641 + 5843990916 = 29629^2 + 76446^2 .

It is a cyclic number.

It is not a de Polignac number, because 6721868557 - 2¹⁹ = 6721344269 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 6721868498 and 6721868507.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6721868537) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 37763218 + ... + 37763395.

It is an arithmetic number, because the mean of its divisors is an integer number (1699348815).

Almost surely, 2^6721868557 is an apocalyptic number.

It is an amenable number.

6721868557 is a deficient number, since it is larger than the sum of its proper divisors (75526703).

6721868557 is an equidigital number, since it uses as much as digits as its factorization.

6721868557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 75526702.

The product of its digits is 5644800, while the sum is 55.

The square root of 6721868557 is about 81987.0023662288. The cubic root of 6721868557 is about 1887.2524822691.

The spelling of 6721868557 in words is "six billion, seven hundred twenty-one million, eight hundred sixty-eight thousand, five hundred fifty-seven".