21280 has 48 divisors (see below), whose sum is σ = 60480. Its totient is φ = 6912.

The previous prime is 21277. The next prime is 21283. The reversal of 21280 is 8212.

It is an interprime number because it is at equal distance from previous prime (21277) and next prime (21283).

It is a nialpdrome in base 16.

It is a self number, because there is not a number n which added to its sum of digits gives 21280.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21283) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1111 + ... + 1129.

It is an arithmetic number, because the mean of its divisors is an integer number (1260).

2²¹²⁸⁰ is an apocalyptic number.

21280 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30240).

21280 is an abundant number, since it is smaller than the sum of its proper divisors (39200).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21280 is a wasteful number, since it uses less digits than its factorization.

21280 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41 (or 33 counting only the distinct ones).

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

The square root of 21280 is about 145.8766602305. The cubic root of 21280 is about 27.7113196447.

Adding to 21280 its product of nonzero digits (32), we get a palindrome (21312).

Adding to 21280 its reverse (8212), we get a palindrome (29492).

It can be divided in two parts, 212 and 80, that added together give a palindrome (292).

The spelling of 21280 in words is "twenty-one thousand, two hundred eighty".