1666891891 has 16 divisors (see below), whose sum is σ = 1926512640. Its totient is φ = 1412722080.

The previous prime is 1666891883. The next prime is 1666891909. The reversal of 1666891891 is 1981986661.

It is not a de Polignac number, because 1666891891 - 2³ = 1666891883 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1666891691) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 273465 + ... + 279493.

It is an arithmetic number, because the mean of its divisors is an integer number (120407040).

Almost surely, 2^1666891891 is an apocalyptic number.

1666891891 is a deficient number, since it is larger than the sum of its proper divisors (259620749).

1666891891 is a wasteful number, since it uses less digits than its factorization.

1666891891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6474.

The product of its digits is 1119744, while the sum is 55.

The square root of 1666891891 is about 40827.5873766746. The cubic root of 1666891891 is about 1185.6845056861.

The spelling of 1666891891 in words is "one billion, six hundred sixty-six million, eight hundred ninety-one thousand, eight hundred ninety-one".