666042721 has 2 divisors, whose sum is σ = 666042722. Its totient is φ = 666042720.

The previous prime is 666042709. The next prime is 666042757. The reversal of 666042721 is 127240666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 487526400 + 178516321 = 22080^2 + 13361^2 .

It is a cyclic number.

It is not a de Polignac number, because 666042721 - 2²³ = 657654113 is a prime.

It is a super-2 number, since 2×666042721² = 887225812394167682, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (666042791) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333021360 + 333021361.

It is an arithmetic number, because the mean of its divisors is an integer number (333021361).

Almost surely, 2^666042721 is an apocalyptic number.

It is an amenable number.

666042721 is a deficient number, since it is larger than the sum of its proper divisors (1).

666042721 is an equidigital number, since it uses as much as digits as its factorization.

666042721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 24192, while the sum is 34.

The square root of 666042721 is about 25807.8034904174. The cubic root of 666042721 is about 873.3078462963.

The spelling of 666042721 in words is "six hundred sixty-six million, forty-two thousand, seven hundred twenty-one".