19911991 has 16 divisors (see below), whose sum is σ = 22303008. Its totient is φ = 17625600.

The previous prime is 19911979. The next prime is 19912001.

19911991 is nontrivially palindromic in base 10.

It is a cyclic number.

It is not a de Polignac number, because 19911991 - 2⁵ = 19911959 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 (19911961) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 109921 + ... + 110101.

It is an arithmetic number, because the mean of its divisors is an integer number (1393938).

Almost surely, 2^19911991 is an apocalyptic number.

19911991 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

19911991 is a deficient number, since it is larger than the sum of its proper divisors (2391017).

19911991 is a wasteful number, since it uses less digits than its factorization.

19911991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 402.

The product of its digits is 6561, while the sum is 40.

The square root of 19911991 is about 4462.2854010025. The cubic root of 19911991 is about 271.0430209067.

It can be divided in two parts, 19911 and 991, that added together give a palindrome (20902).

The spelling of 19911991 in words is "nineteen million, nine hundred eleven thousand, nine hundred ninety-one".