665204821 has 2 divisors, whose sum is σ = 665204822. Its totient is φ = 665204820.

The previous prime is 665204809. The next prime is 665204831. The reversal of 665204821 is 128402566.

665204821 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 548262225 + 116942596 = 23415^2 + 10814^2 .

It is a cyclic number.

It is not a de Polignac number, because 665204821 - 2¹¹ = 665202773 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (665204831) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332602410 + 332602411.

It is an arithmetic number, because the mean of its divisors is an integer number (332602411).

Almost surely, 2^665204821 is an apocalyptic number.

It is an amenable number.

665204821 is a deficient number, since it is larger than the sum of its proper divisors (1).

665204821 is an equidigital number, since it uses as much as digits as its factorization.

665204821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 23040, while the sum is 34.

The square root of 665204821 is about 25791.5649195624. The cubic root of 665204821 is about 872.9414775497.

The spelling of 665204821 in words is "six hundred sixty-five million, two hundred four thousand, eight hundred twenty-one".