1666388861 has 4 divisors (see below), whose sum is σ = 1694632800. Its totient is φ = 1638144924.

The previous prime is 1666388837. The next prime is 1666388879. The reversal of 1666388861 is 1688836661.

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 1666388861 - 2³⁰ = 592647037 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1666388821) 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 3 ways as a sum of consecutive naturals, for example, 14121881 + ... + 14121998.

It is an arithmetic number, because the mean of its divisors is an integer number (423658200).

Almost surely, 2^1666388861 is an apocalyptic number.

It is an amenable number.

1666388861 is a deficient number, since it is larger than the sum of its proper divisors (28243939).

1666388861 is an equidigital number, since it uses as much as digits as its factorization.

1666388861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28243938.

The product of its digits is 1990656, while the sum is 53.

The square root of 1666388861 is about 40821.4264939382. The cubic root of 1666388861 is about 1185.5652228285.

The spelling of 1666388861 in words is "one billion, six hundred sixty-six million, three hundred eighty-eight thousand, eight hundred sixty-one".