666658561 has 2 divisors, whose sum is σ = 666658562. Its totient is φ = 666658560.

The previous prime is 666658549. The next prime is 666658633. The reversal of 666658561 is 165856666.

666658561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 418407025 + 248251536 = 20455^2 + 15756^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-666658561 is a prime.

It is not a weakly prime, because it can be changed into another prime (666658661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333329280 + 333329281.

It is an arithmetic number, because the mean of its divisors is an integer number (333329281).

Almost surely, 2^666658561 is an apocalyptic number.

It is an amenable number.

666658561 is a deficient number, since it is larger than the sum of its proper divisors (1).

666658561 is an equidigital number, since it uses as much as digits as its factorization.

666658561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1555200, while the sum is 49.

The square root of 666658561 is about 25819.7320086789. The cubic root of 666658561 is about 873.5769242459.

The spelling of 666658561 in words is "six hundred sixty-six million, six hundred fifty-eight thousand, five hundred sixty-one".