21305280 has 56 divisors (see below), whose sum is σ = 67647312. Its totient is φ = 5681152.

The previous prime is 21305279. The next prime is 21305293. The reversal of 21305280 is 8250312.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10137 + ... + 12056.

Almost surely, 2^21305280 is an apocalyptic number.

21305280 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21305280 is an abundant number, since it is smaller than the sum of its proper divisors (46342032).

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

21305280 is a wasteful number, since it uses less digits than its factorization.

21305280 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22213 (or 22203 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 21.

The square root of 21305280 is about 4615.7642920756. The cubic root of 21305280 is about 277.2228870700. Note that the first 3 decimals are identical.

Adding to 21305280 its reverse (8250312), we get a palindrome (29555592).

The spelling of 21305280 in words is "twenty-one million, three hundred five thousand, two hundred eighty".