861991491861 has 24 divisors (see below), whose sum is σ = 1245935320344. Its totient is φ = 574275087360.

The previous prime is 861991491859. The next prime is 861991491887. The reversal of 861991491861 is 168194199168.

861991491861 is a `hidden beast` number, since 8 + 61 + 9 + 9 + 1 + 491 + 86 + 1 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 348225091236 + 513766400625 = 590106^2 + 716775^2 .

It is not a de Polignac number, because 861991491861 - 2¹ = 861991491859 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (861991491661) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 137322255 + ... + 137328531.

It is an arithmetic number, because the mean of its divisors is an integer number (51913971681).

Almost surely, 2^861991491861 is an apocalyptic number.

It is an amenable number.

861991491861 is a deficient number, since it is larger than the sum of its proper divisors (383943828483).

861991491861 is a wasteful number, since it uses less digits than its factorization.

861991491861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14101 (or 14098 counting only the distinct ones).

The product of its digits is 6718464, while the sum is 63.

The spelling of 861991491861 in words is "eight hundred sixty-one billion, nine hundred ninety-one million, four hundred ninety-one thousand, eight hundred sixty-one".