19131991 has 4 divisors (see below), whose sum is σ = 19749184. Its totient is φ = 18514800.

The previous prime is 19131977. The next prime is 19132013. The reversal of 19131991 is 19913191.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19913191 = 31 ⋅642361.

It is a cyclic number.

It is not a de Polignac number, because 19131991 - 2¹³ = 19123799 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19131191) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 308550 + ... + 308611.

It is an arithmetic number, because the mean of its divisors is an integer number (4937296).

Almost surely, 2^19131991 is an apocalyptic number.

19131991 is a deficient number, since it is larger than the sum of its proper divisors (617193).

19131991 is an equidigital number, since it uses as much as digits as its factorization.

19131991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 617192.

The product of its digits is 2187, while the sum is 34.

The square root of 19131991 is about 4374.0131458422. The cubic root of 19131991 is about 267.4566430443.

The spelling of 19131991 in words is "nineteen million, one hundred thirty-one thousand, nine hundred ninety-one".