665967721 has 2 divisors, whose sum is σ = 665967722. Its totient is φ = 665967720.

The previous prime is 665967671. The next prime is 665967749. The reversal of 665967721 is 127769566.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 665898025 + 69696 = 25805^2 + 264^2 .

It is a cyclic number.

It is not a de Polignac number, because 665967721 - 2¹³ = 665959529 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (665967791) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332983860 + 332983861.

It is an arithmetic number, because the mean of its divisors is an integer number (332983861).

Almost surely, 2^665967721 is an apocalyptic number.

It is an amenable number.

665967721 is a deficient number, since it is larger than the sum of its proper divisors (1).

665967721 is an equidigital number, since it uses as much as digits as its factorization.

665967721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 952560, while the sum is 49.

The square root of 665967721 is about 25806.3504006281. The cubic root of 665967721 is about 873.2750653425.

The spelling of 665967721 in words is "six hundred sixty-five million, nine hundred sixty-seven thousand, seven hundred twenty-one".