19121991 has 32 divisors (see below), whose sum is σ = 31933440. Its totient is φ = 9924096.

The previous prime is 19121987. The next prime is 19122013. The reversal of 19121991 is 19912191.

It is not a de Polignac number, because 19121991 - 2² = 19121987 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19121981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 9430 + ... + 11276.

It is an arithmetic number, because the mean of its divisors is an integer number (997920).

Almost surely, 2^19121991 is an apocalyptic number.

19121991 is a deficient number, since it is larger than the sum of its proper divisors (12811449).

19121991 is a wasteful number, since it uses less digits than its factorization.

19121991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1903.

The product of its digits is 1458, while the sum is 33.

The square root of 19121991 is about 4372.8698814394. The cubic root of 19121991 is about 267.4100364200.

The spelling of 19121991 in words is "nineteen million, one hundred twenty-one thousand, nine hundred ninety-one".