19971811 has 4 divisors (see below), whose sum is σ = 20106000. Its totient is φ = 19837624.

The previous prime is 19971761. The next prime is 19971857. The reversal of 19971811 is 11817991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 11817991 = 43 ⋅274837.

It is a cyclic number.

It is not a de Polignac number, because 19971811 - 2⁷ = 19971683 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (11971811) 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, 66871 + ... + 67168.

It is an arithmetic number, because the mean of its divisors is an integer number (5026500).

Almost surely, 2^19971811 is an apocalyptic number.

19971811 is a deficient number, since it is larger than the sum of its proper divisors (134189).

19971811 is a wasteful number, since it uses less digits than its factorization.

19971811 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 134188.

The product of its digits is 4536, while the sum is 37.

The square root of 19971811 is about 4468.9832176906. The cubic root of 19971811 is about 271.3141738342.

It can be divided in two parts, 199 and 71811, that added together give a triangular number (72010 = T₃₇₉).

The spelling of 19971811 in words is "nineteen million, nine hundred seventy-one thousand, eight hundred eleven".