6721218661 has 2 divisors, whose sum is σ = 6721218662. Its totient is φ = 6721218660.

The previous prime is 6721218659. The next prime is 6721218743. The reversal of 6721218661 is 1668121276.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 4669672225 + 2051546436 = 68335^2 + 45294^2 .

It is a cyclic number.

It is not a de Polignac number, because 6721218661 - 2¹ = 6721218659 is a prime.

Together with 6721218659, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6721218641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3360609330 + 3360609331.

It is an arithmetic number, because the mean of its divisors is an integer number (3360609331).

Almost surely, 2^6721218661 is an apocalyptic number.

It is an amenable number.

6721218661 is a deficient number, since it is larger than the sum of its proper divisors (1).

6721218661 is an equidigital number, since it uses as much as digits as its factorization.

6721218661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 48384, while the sum is 40.

The square root of 6721218661 is about 81983.0388617060. The cubic root of 6721218661 is about 1887.1916580425.

The spelling of 6721218661 in words is "six billion, seven hundred twenty-one million, two hundred eighteen thousand, six hundred sixty-one".