1666065561 has 4 divisors (see below), whose sum is σ = 2221420752. Its totient is φ = 1110710372.

The previous prime is 1666065551. The next prime is 1666065587. The reversal of 1666065561 is 1655606661.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1666065561 - 2⁶ = 1666065497 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (1666065551) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 277677591 + ... + 277677596.

It is an arithmetic number, because the mean of its divisors is an integer number (555355188).

Almost surely, 2^1666065561 is an apocalyptic number.

It is an amenable number.

1666065561 is a deficient number, since it is larger than the sum of its proper divisors (555355191).

1666065561 is an equidigital number, since it uses as much as digits as its factorization.

1666065561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 555355190.

The product of its (nonzero) digits is 194400, while the sum is 42.

The square root of 1666065561 is about 40817.4663716405. The cubic root of 1666065561 is about 1185.4885464424.

The spelling of 1666065561 in words is "one billion, six hundred sixty-six million, sixty-five thousand, five hundred sixty-one".