21686616 has 120 divisors (see below), whose sum is σ = 70763220. Its totient is φ = 6187104.

The previous prime is 21686591. The next prime is 21686617. The reversal of 21686616 is 61668612.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21686617) by changing a digit.

It is a polite number, since it can be written in 29 ways as a sum of consecutive naturals, for example, 31411 + ... + 32093.

Almost surely, 2^21686616 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 21686616, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35381610).

21686616 is an abundant number, since it is smaller than the sum of its proper divisors (49076604).

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

21686616 is a wasteful number, since it uses less digits than its factorization.

21686616 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 715 (or 695 counting only the distinct ones).

The product of its digits is 20736, while the sum is 36.

The square root of 21686616 is about 4656.8890903692. The cubic root of 21686616 is about 278.8670889654.

The spelling of 21686616 in words is "twenty-one million, six hundred eighty-six thousand, six hundred sixteen".