665016721 has 2 divisors, whose sum is σ = 665016722. Its totient is φ = 665016720.

The previous prime is 665016673. The next prime is 665016731. The reversal of 665016721 is 127610566.

It is a happy number.

665016721 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., 664608400 + 408321 = 25780^2 + 639^2 .

It is a cyclic number.

It is not a de Polignac number, because 665016721 - 2⁷ = 665016593 is a prime.

It is not a weakly prime, because it can be changed into another prime (665016731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332508360 + 332508361.

It is an arithmetic number, because the mean of its divisors is an integer number (332508361).

Almost surely, 2^665016721 is an apocalyptic number.

It is an amenable number.

665016721 is a deficient number, since it is larger than the sum of its proper divisors (1).

665016721 is an equidigital number, since it uses as much as digits as its factorization.

665016721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 15120, while the sum is 34.

The square root of 665016721 is about 25787.9181207014. The cubic root of 665016721 is about 872.8591892248.

The spelling of 665016721 in words is "six hundred sixty-five million, sixteen thousand, seven hundred twenty-one".