1991190209921 has 8 divisors (see below), whose sum is σ = 2172230755488. Its totient is φ = 1810153540000.

The previous prime is 1991190209861. The next prime is 1991190209951. The reversal of 1991190209921 is 1299020911991.

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

It is a cyclic number.

It is not a de Polignac number, because 1991190209921 - 2¹⁰ = 1991190208897 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1991190209951) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 162821 + ... + 2002221.

It is an arithmetic number, because the mean of its divisors is an integer number (271528844436).

Almost surely, 2^{1991190209921} is an apocalyptic number.

1991190209921 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1991190209921 is a deficient number, since it is larger than the sum of its proper divisors (181040545567).

1991190209921 is a wasteful number, since it uses less digits than its factorization.

1991190209921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1937823.

The product of its (nonzero) digits is 236196, while the sum is 53.

The spelling of 1991190209921 in words is "one trillion, nine hundred ninety-one billion, one hundred ninety million, two hundred nine thousand, nine hundred twenty-one".