21616 has 20 divisors (see below), whose sum is σ = 48112. Its totient is φ = 9216.

The previous prime is 21613. The next prime is 21617. The reversal of 21616 is 61612.

21616 is an esthetic number in base 13, because in such base its adjacent digits differ by 1.

It is a Harshad number since it is a multiple of its sum of digits (16).

It is an alternating number because its digits alternate between even and odd.

It is a nialpdrome in base 15.

It is a zygodrome in base 15.

It is a self number, because there is not a number n which added to its sum of digits gives 21616.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21611) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16 + ... + 208.

2²¹⁶¹⁶ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21616, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24056).

21616 is an abundant number, since it is smaller than the sum of its proper divisors (26496).

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

21616 is a wasteful number, since it uses less digits than its factorization.

21616 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 208 (or 202 counting only the distinct ones).

The product of its digits is 72, while the sum is 16.

The square root of 21616 is about 147.0238075959. The cubic root of 21616 is about 27.8564077324.

It can be divided in two parts, 216 and 16, that added together give a palindrome (232).

The spelling of 21616 in words is "twenty-one thousand, six hundred sixteen".