19881 has 9 divisors (see below), whose sum is σ = 29341.
Its totient is φ = 12972.
The previous prime is 19867. The next prime is 19889. The reversal of 19881 is 18891.
19881 = T140 + T141.
The square root of 19881 is 141.
It is a perfect power (a square), and thus also a powerful number.
It is a tau number, because it is divible by the number of its divisors (9).
It is not a de Polignac number, because 19881 - 27 = 19753 is a prime.
It is a super-2 number, since 2×198812 = 790508322, which contains 22 as substring.
It is a Duffinian number.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 19881.
It is not an unprimeable number, because it can be changed into a prime (19889) by changing a digit.
It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 400 + ... + 446.
219881 is an apocalyptic number.
19881 is the 141-st square number.
19881 is the 71-st centered octagonal number.
It is an amenable number.
19881 is a deficient number, since it is larger than the sum of its proper divisors (9460).
19881 is an equidigital number, since it uses as much as digits as its factorization.
19881 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 100 (or 50 counting only the distinct ones).
The product of its digits is 576, while the sum is 27.
The cubic root of 19881 is about 27.0902330876.
Multiplying 19881 by its product of digits (576), we get a square (11451456 = 33842).
Subtracting from 19881 its reverse (18891), we obtain a triangular number (990 = T44).
It can be divided in two parts, 19 and 881, that added together give a square (900 = 302).
The spelling of 19881 in words is "nineteen thousand, eight hundred eighty-one".