19991991 has 32 divisors (see below), whose sum is σ = 29352960. Its totient is φ = 12063744.

The previous prime is 19991989. The next prime is 19992001. The reversal of 19991991 is 19919991.

It is not a de Polignac number, because 19991991 - 2¹ = 19991989 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 19991991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19991911) 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, 194046 + ... + 194148.

It is an arithmetic number, because the mean of its divisors is an integer number (917280).

Almost surely, 2^19991991 is an apocalyptic number.

19991991 is a deficient number, since it is larger than the sum of its proper divisors (9360969).

19991991 is a wasteful number, since it uses less digits than its factorization.

19991991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 255.

The product of its digits is 59049, while the sum is 48.

The square root of 19991991 is about 4471.2404319160. The cubic root of 19991991 is about 271.4055238708.

The spelling of 19991991 in words is "nineteen million, nine hundred ninety-one thousand, nine hundred ninety-one".