665612821 has 2 divisors, whose sum is σ = 665612822. Its totient is φ = 665612820.

The previous prime is 665612789. The next prime is 665612833. The reversal of 665612821 is 128216566.

665612821 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., 487923921 + 177688900 = 22089^2 + 13330^2 .

It is a cyclic number.

It is not a de Polignac number, because 665612821 - 2⁵ = 665612789 is a prime.

It is a Chen prime.

It is equal to p_34562566 and since 665612821 and 34562566 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (665612861) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332806410 + 332806411.

It is an arithmetic number, because the mean of its divisors is an integer number (332806411).

Almost surely, 2^665612821 is an apocalyptic number.

It is an amenable number.

665612821 is a deficient number, since it is larger than the sum of its proper divisors (1).

665612821 is an equidigital number, since it uses as much as digits as its factorization.

665612821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 34560, while the sum is 37.

The square root of 665612821 is about 25799.4732698170. The cubic root of 665612821 is about 873.1199124819.

The spelling of 665612821 in words is "six hundred sixty-five million, six hundred twelve thousand, eight hundred twenty-one".