1991401489791 has 16 divisors (see below), whose sum is σ = 3371685062400. Its totient is φ = 1137943708344.

The previous prime is 1991401489697. The next prime is 1991401489837. The reversal of 1991401489791 is 1979841041991.

1991401489791 is a `hidden beast` number, since 1 + 9 + 9 + 140 + 1 + 489 + 7 + 9 + 1 = 666.

It is not a de Polignac number, because 1991401489791 - 2¹¹ = 1991401487743 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (63).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991401489391) 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, 5268257721 + ... + 5268258098.

It is an arithmetic number, because the mean of its divisors is an integer number (210730316400).

Almost surely, 2^{1991401489791} is an apocalyptic number.

1991401489791 is a deficient number, since it is larger than the sum of its proper divisors (1380283572609).

1991401489791 is a wasteful number, since it uses less digits than its factorization.

1991401489791 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10536515835 (or 10536515829 counting only the distinct ones).

The product of its (nonzero) digits is 5878656, while the sum is 63.

The spelling of 1991401489791 in words is "one trillion, nine hundred ninety-one billion, four hundred one million, four hundred eighty-nine thousand, seven hundred ninety-one".