664838811821 has 2 divisors, whose sum is σ = 664838811822. Its totient is φ = 664838811820.

The previous prime is 664838811811. The next prime is 664838811841. The reversal of 664838811821 is 128118838466.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 557539982596 + 107298829225 = 746686^2 + 327565^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-664838811821 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (664838811811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332419405910 + 332419405911.

It is an arithmetic number, because the mean of its divisors is an integer number (332419405911).

Almost surely, 2^664838811821 is an apocalyptic number.

It is an amenable number.

664838811821 is a deficient number, since it is larger than the sum of its proper divisors (1).

664838811821 is an equidigital number, since it uses as much as digits as its factorization.

664838811821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3538944, while the sum is 56.

The spelling of 664838811821 in words is "six hundred sixty-four billion, eight hundred thirty-eight million, eight hundred eleven thousand, eight hundred twenty-one".