861291891 has 12 divisors (see below), whose sum is σ = 1259837280. Its totient is φ = 566925840.

The previous prime is 861291881. The next prime is 861291911. The reversal of 861291891 is 198192168.

It is not a de Polignac number, because 861291891 - 2¹⁵ = 861259123 is a prime.

It is not an unprimeable number, because it can be changed into a prime (861291811) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 604980 + ... + 606401.

It is an arithmetic number, because the mean of its divisors is an integer number (104986440).

Almost surely, 2^861291891 is an apocalyptic number.

861291891 is a deficient number, since it is larger than the sum of its proper divisors (398545389).

861291891 is a wasteful number, since it uses less digits than its factorization.

861291891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1211466 (or 1211463 counting only the distinct ones).

The product of its digits is 62208, while the sum is 45.

The square root of 861291891 is about 29347.7748901003. The cubic root of 861291891 is about 951.4444843439. Note that the first 4 decimals are identical.

The spelling of 861291891 in words is "eight hundred sixty-one million, two hundred ninety-one thousand, eight hundred ninety-one".