21009280 has 64 divisors (see below), whose sum is σ = 53207280. Its totient is φ = 7905280.

The previous prime is 21009277. The next prime is 21009283. The reversal of 21009280 is 8290012.

It is an interprime number because it is at equal distance from previous prime (21009277) and next prime (21009283).

It is a tau number, because it is divible by the number of its divisors (64).

It is a super-2 number, since 2×21009280² = 882779692236800, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21009283) 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 in 7 ways as a sum of consecutive naturals, for example, 9915 + ... + 11845.

Almost surely, 2^21009280 is an apocalyptic number.

21009280 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 21009280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26603640).

21009280 is an abundant number, since it is smaller than the sum of its proper divisors (32198000).

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

21009280 is a wasteful number, since it uses less digits than its factorization.

21009280 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1967 (or 1955 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 22.

The square root of 21009280 is about 4583.5881141307. The cubic root of 21009280 is about 275.9330510444.

Adding to 21009280 its reverse (8290012), we get a palindrome (29299292).

The spelling of 21009280 in words is "twenty-one million, nine thousand, two hundred eighty".