666541561 has 6 divisors (see below), whose sum is σ = 775364730. Its totient is φ = 571321296.

The previous prime is 666541553. The next prime is 666541567. The reversal of 666541561 is 165145666.

It can be written as a sum of positive squares in only one way, i.e., 637865536 + 28676025 = 25256^2 + 5355^2 .

It is not a de Polignac number, because 666541561 - 2³ = 666541553 is a prime.

It is not an unprimeable number, because it can be changed into a prime (666541567) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 6801396 + ... + 6801493.

It is an arithmetic number, because the mean of its divisors is an integer number (129227455).

Almost surely, 2^666541561 is an apocalyptic number.

It is an amenable number.

666541561 is a deficient number, since it is larger than the sum of its proper divisors (108823169).

666541561 is a wasteful number, since it uses less digits than its factorization.

666541561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13602903 (or 13602896 counting only the distinct ones).

The product of its digits is 129600, while the sum is 40.

The square root of 666541561 is about 25817.4662002296. The cubic root of 666541561 is about 873.5258163845.

The spelling of 666541561 in words is "six hundred sixty-six million, five hundred forty-one thousand, five hundred sixty-one".