19945 has 4 divisors (see below), whose sum is σ = 23940. Its totient is φ = 15952.

The previous prime is 19937. The next prime is 19949. The reversal of 19945 is 54991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 54991 = 127 ⋅433.

It can be written as a sum of positive squares in 2 ways, for example, as 8281 + 11664 = 91^2 + 108^2 .

It is a cyclic number.

It is not a de Polignac number, because 19945 - 2³ = 19937 is a prime.

It is a nialpdrome in base 12.

It is not an unprimeable number, because it can be changed into a prime (19949) 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, 1990 + ... + 1999.

It is an arithmetic number, because the mean of its divisors is an integer number (5985).

2¹⁹⁹⁴⁵ is an apocalyptic number.

It is an amenable number.

19945 is a deficient number, since it is larger than the sum of its proper divisors (3995).

19945 is an equidigital number, since it uses as much as digits as its factorization.

19945 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3994.

The product of its digits is 1620, while the sum is 28.

The square root of 19945 is about 141.2267680010. The cubic root of 19945 is about 27.1192711609.

It can be divided in two parts, 19 and 945, that multiplied together give a triangular number (17955 = T₁₈₉).

The spelling of 19945 in words is "nineteen thousand, nine hundred forty-five".