20281 has 4 divisors (see below), whose sum is σ = 21492. Its totient is φ = 19072.

The previous prime is 20269. The next prime is 20287. The reversal of 20281 is 18202.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 13225 + 7056 = 115^2 + 84^2 .

It is a cyclic number.

It is not a de Polignac number, because 20281 - 2⁵ = 20249 is a prime.

It is a super-2 number, since 2×20281² = 822637922, which contains 22 as substring.

It is a Duffinian number.

It is a zygodrome in base 5.

It is not an unprimeable number, because it can be changed into a prime (20287) 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, 580 + ... + 613.

It is an arithmetic number, because the mean of its divisors is an integer number (5373).

2²⁰²⁸¹ is an apocalyptic number.

It is an amenable number.

20281 is a deficient number, since it is larger than the sum of its proper divisors (1211).

20281 is a wasteful number, since it uses less digits than its factorization.

20281 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1210.

The product of its (nonzero) digits is 32, while the sum is 13.

The square root of 20281 is about 142.4113759501. The cubic root of 20281 is about 27.2707106253.

Adding to 20281 its reverse (18202), we get a palindrome (38483).

The spelling of 20281 in words is "twenty thousand, two hundred eighty-one".