21608 has 16 divisors (see below), whose sum is σ = 42180. Its totient is φ = 10368.

The previous prime is 21601. The next prime is 21611. The reversal of 21608 is 80612.

It is a Cunningham number, because it is equal to 147²-1.

It can be written as a sum of positive squares in 2 ways, for example, as 20164 + 1444 = 142^2 + 38^2 .

It is a plaindrome in base 7.

It is a zygodrome in base 7.

It is not an unprimeable number, because it can be changed into a prime (21601) by changing a digit.

21608 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 260 + ... + 332.

2²¹⁶⁰⁸ is an apocalyptic number.

It is an amenable number.

21608 is a deficient number, since it is larger than the sum of its proper divisors (20572).

21608 is a wasteful number, since it uses less digits than its factorization.

21608 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 116 (or 112 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 17.

The square root of 21608 is about 146.9965986001. The cubic root of 21608 is about 27.8529707912.

Subtracting from 21608 its product of nonzero digits (96), we obtain a palindrome (21512).

The spelling of 21608 in words is "twenty-one thousand, six hundred eight".