12191920921 has 4 divisors (see below), whose sum is σ = 12210366244. Its totient is φ = 12173475600.

The previous prime is 12191920913. The next prime is 12191920967. The reversal of 12191920921 is 12902919121.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12902919121 = 85037 ⋅151733.

It can be written as a sum of positive squares in 2 ways, for example, as 4507645321 + 7684275600 = 67139^2 + 87660^2 .

It is a cyclic number.

It is not a de Polignac number, because 12191920921 - 2³ = 12191920913 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (12191920121) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9221670 + ... + 9222991.

It is an arithmetic number, because the mean of its divisors is an integer number (3052591561).

Almost surely, 2^12191920921 is an apocalyptic number.

It is an amenable number.

12191920921 is a deficient number, since it is larger than the sum of its proper divisors (18445323).

12191920921 is an equidigital number, since it uses as much as digits as its factorization.

12191920921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18445322.

The product of its (nonzero) digits is 5832, while the sum is 37.

The spelling of 12191920921 in words is "twelve billion, one hundred ninety-one million, nine hundred twenty thousand, nine hundred twenty-one".