19681 has 2 divisors, whose sum is σ = 19682. Its totient is φ = 19680.

The previous prime is 19661. The next prime is 19687. The reversal of 19681 is 18691.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19600 + 81 = 140^2 + 9^2 .

It is an emirp because it is prime and its reverse (18691) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 19681 - 2⁷ = 19553 is a prime.

It is a super-2 number, since 2×19681² = 774683522, which contains 22 as substring.

It is an Ulam number.

It is a plaindrome in base 7.

It is a nialpdrome in base 3.

It is a zygodrome in base 5.

It is not a weakly prime, because it can be changed into another prime (19687) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9840 + 9841.

It is an arithmetic number, because the mean of its divisors is an integer number (9841).

2¹⁹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

19681 is a deficient number, since it is larger than the sum of its proper divisors (1).

19681 is an equidigital number, since it uses as much as digits as its factorization.

19681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 432, while the sum is 25.

The square root of 19681 is about 140.2889874509. The cubic root of 19681 is about 26.9990854743. Note that the first 3 decimals are identical.

Subtracting from 19681 its reverse (18691), we obtain a triangular number (990 = T₄₄).

It can be divided in two parts, 196 and 81, that multiplied together give a square (15876 = 126²).

The spelling of 19681 in words is "nineteen thousand, six hundred eighty-one".