666655561 has 32 divisors (see below), whose sum is σ = 841857408. Its totient is φ = 518538240.

The previous prime is 666655559. The next prime is 666655579. The reversal of 666655561 is 165556666.

It is not a de Polignac number, because 666655561 - 2¹ = 666655559 is a prime.

It is not an unprimeable number, because it can be changed into a prime (666655511) 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 in 31 ways as a sum of consecutive naturals, for example, 160831 + ... + 164923.

It is an arithmetic number, because the mean of its divisors is an integer number (26308044).

Almost surely, 2^666655561 is an apocalyptic number.

It is an amenable number.

666655561 is a deficient number, since it is larger than the sum of its proper divisors (175201847).

666655561 is a wasteful number, since it uses less digits than its factorization.

666655561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4201.

The product of its digits is 972000, while the sum is 46.

The square root of 666655561 is about 25819.6739135102. The cubic root of 666655561 is about 873.5756138626.

The spelling of 666655561 in words is "six hundred sixty-six million, six hundred fifty-five thousand, five hundred sixty-one".