21280320 has 140 divisors (see below), whose sum is σ = 75790044. Its totient is φ = 5667840.

The previous prime is 21280307. The next prime is 21280327. The reversal of 21280320 is 2308212.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 6718464 + 14561856 = 2592^2 + 3816^2 .

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21280293 and 21280302.

It is not an unprimeable number, because it can be changed into a prime (21280327) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 25510 + ... + 26330.

Almost surely, 2^21280320 is an apocalyptic number.

21280320 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 21280320, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37895022).

21280320 is an abundant number, since it is smaller than the sum of its proper divisors (54509724).

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

21280320 is an equidigital number, since it uses as much as digits as its factorization.

21280320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 850 (or 831 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 18.

The square root of 21280320 is about 4613.0597221367. The cubic root of 21280320 is about 277.1145854788.

Adding to 21280320 its reverse (2308212), we get a palindrome (23588532).

The spelling of 21280320 in words is "twenty-one million, two hundred eighty thousand, three hundred twenty".