21308 has 12 divisors (see below), whose sum is σ = 42672. Its totient is φ = 9120.

The previous prime is 21283. The next prime is 21313. The reversal of 21308 is 80312.

21308 is an admirable number.

It is a Harshad number since it is a multiple of its sum of digits (14).

It is a nialpdrome in base 13.

It is a zygodrome in base 13.

It is a junction number, because it is equal to n+sod(n) for n = 21292 and 21301.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 353 + ... + 408.

It is an arithmetic number, because the mean of its divisors is an integer number (3556).

2²¹³⁰⁸ is an apocalyptic number.

21308 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21308 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

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

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21336).

21308 is a wasteful number, since it uses less digits than its factorization.

21308 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 772 (or 770 counting only the distinct ones).

The product of its (nonzero) digits is 48, while the sum is 14.

The square root of 21308 is about 145.9726001687. The cubic root of 21308 is about 27.7234684054.

The spelling of 21308 in words is "twenty-one thousand, three hundred eight".