19991871 has 12 divisors (see below), whose sum is σ = 28958280. Its totient is φ = 13290480.

The previous prime is 19991863. The next prime is 19991879. The reversal of 19991871 is 17819991.

It is an interprime number because it is at equal distance from previous prime (19991863) and next prime (19991879).

It is not a de Polignac number, because 19991871 - 2³ = 19991863 is a prime.

It is a Smith number, since the sum of its digits (45) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19991879) 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 11 ways as a sum of consecutive naturals, for example, 481 + ... + 6341.

It is an arithmetic number, because the mean of its divisors is an integer number (2413190).

Almost surely, 2^19991871 is an apocalyptic number.

19991871 is a deficient number, since it is larger than the sum of its proper divisors (8966409).

19991871 is a wasteful number, since it uses less digits than its factorization.

19991871 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6246 (or 6243 counting only the distinct ones).

The product of its digits is 40824, while the sum is 45.

The square root of 19991871 is about 4471.2270128008. The cubic root of 19991871 is about 271.4049808412.

The spelling of 19991871 in words is "nineteen million, nine hundred ninety-one thousand, eight hundred seventy-one".