21305680 has 120 divisors (see below), whose sum is σ = 56996352. Its totient is φ = 7392000.

The previous prime is 21305671. The next prime is 21305681. The reversal of 21305680 is 8650312.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21305681) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 300045 + ... + 300115.

Almost surely, 2^21305680 is an apocalyptic number.

21305680 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 21305680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28498176).

21305680 is an abundant number, since it is smaller than the sum of its proper divisors (35690672).

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

21305680 is a wasteful number, since it uses less digits than its factorization.

21305680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 137 (or 120 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 21305680 is about 4615.8076216411. The cubic root of 21305680 is about 277.2246219836.

Adding to 21305680 its reverse (8650312), we get a palindrome (29955992).

The spelling of 21305680 in words is "twenty-one million, three hundred five thousand, six hundred eighty".