666403561 has 2 divisors, whose sum is σ = 666403562. Its totient is φ = 666403560.

The previous prime is 666403513. The next prime is 666403651. The reversal of 666403561 is 165304666.

666403561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

Together with next prime (666403651) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 663320025 + 3083536 = 25755^2 + 1756^2 .

It is a cyclic number.

It is not a de Polignac number, because 666403561 - 2⁷ = 666403433 is a prime.

It is a super-2 number, since 2×666403561² = 888187412226961442, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 666403561.

It is not a weakly prime, because it can be changed into another prime (666403501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333201780 + 333201781.

It is an arithmetic number, because the mean of its divisors is an integer number (333201781).

Almost surely, 2^666403561 is an apocalyptic number.

It is an amenable number.

666403561 is a deficient number, since it is larger than the sum of its proper divisors (1).

666403561 is an equidigital number, since it uses as much as digits as its factorization.

666403561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 77760, while the sum is 37.

The square root of 666403561 is about 25814.7934525923. The cubic root of 666403561 is about 873.4655276294.

The spelling of 666403561 in words is "six hundred sixty-six million, four hundred three thousand, five hundred sixty-one".