1991388791972 has 24 divisors (see below), whose sum is σ = 3493147996800. Its totient is φ = 993346871616.

The previous prime is 1991388791927. The next prime is 1991388791989. The reversal of 1991388791972 is 2791978831991.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 1991388791972.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 26272304 + ... + 26347992.

It is an arithmetic number, because the mean of its divisors is an integer number (145547833200).

Almost surely, 2^{1991388791972} is an apocalyptic number.

It is an amenable number.

1991388791972 is a deficient number, since it is larger than the sum of its proper divisors (1501759204828).

1991388791972 is a wasteful number, since it uses less digits than its factorization.

1991388791972 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 91115 (or 91113 counting only the distinct ones).

The product of its digits is 123451776, while the sum is 74.

The spelling of 1991388791972 in words is "one trillion, nine hundred ninety-one billion, three hundred eighty-eight million, seven hundred ninety-one thousand, nine hundred seventy-two".