21686720 has 112 divisors (see below), whose sum is σ = 57826656. Its totient is φ = 7680000.

The previous prime is 21686671. The next prime is 21686741. The reversal of 21686720 is 2768612.

It is a Harshad number since it is a multiple of its sum of digits (32).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 214670 + ... + 214770.

Almost surely, 2^21686720 is an apocalyptic number.

21686720 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 21686720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28913328).

21686720 is an abundant number, since it is smaller than the sum of its proper divisors (36139936).

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

21686720 is a wasteful number, since it uses less digits than its factorization.

21686720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 190 (or 180 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 32.

The square root of 21686720 is about 4656.9002566085. The cubic root of 21686720 is about 278.8675347415.

It can be divided in two parts, 2168 and 6720, that added together give a palindrome (8888).

The spelling of 21686720 in words is "twenty-one million, six hundred eighty-six thousand, seven hundred twenty".