1821801991991 has 8 divisors (see below), whose sum is σ = 1827936810240. Its totient is φ = 1815675372288.

The previous prime is 1821801991981. The next prime is 1821801991993. The reversal of 1821801991991 is 1991991081281.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1821801991991 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1821801991991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1821801991993) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1604306 + ... + 2493471.

It is an arithmetic number, because the mean of its divisors is an integer number (228492101280).

Almost surely, 2^{1821801991991} is an apocalyptic number.

1821801991991 is a deficient number, since it is larger than the sum of its proper divisors (6134818249).

1821801991991 is a wasteful number, since it uses less digits than its factorization.

1821801991991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4099273.

The product of its (nonzero) digits is 839808, while the sum is 59.

The spelling of 1821801991991 in words is "one trillion, eight hundred twenty-one billion, eight hundred one million, nine hundred ninety-one thousand, nine hundred ninety-one".