861999891 has 8 divisors (see below), whose sum is σ = 1149477840. Its totient is φ = 574594272.

The previous prime is 861999839. The next prime is 861999913. The reversal of 861999891 is 198999168.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 861999891 - 2⁹ = 861999379 is a prime.

It is not an unprimeable number, because it can be changed into a prime (861999091) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 23181 + ... + 47553.

It is an arithmetic number, because the mean of its divisors is an integer number (143684730).

Almost surely, 2^861999891 is an apocalyptic number.

861999891 is a deficient number, since it is larger than the sum of its proper divisors (287477949).

861999891 is a wasteful number, since it uses less digits than its factorization.

861999891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36165.

The product of its digits is 2519424, while the sum is 60.

The square root of 861999891 is about 29359.8346555290. The cubic root of 861999891 is about 951.7051153831.

The spelling of 861999891 in words is "eight hundred sixty-one million, nine hundred ninety-nine thousand, eight hundred ninety-one".