21688128 has 224 divisors, whose sum is σ = 79979520. Its totient is φ = 5598720.

The previous prime is 21688111. The next prime is 21688159. The reversal of 21688128 is 82188612.

It is a tau number, because it is divible by the number of its divisors (224).

It is a super-2 number, since 2×21688128² = 940749792288768, which contains 22 as substring.

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 junction number, because it is equal to n+sod(n) for n = 21688092 and 21688101.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 132975 + ... + 133137.

Almost surely, 2^21688128 is an apocalyptic number.

21688128 is a gapful number since it is divisible by the number (28) 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 21688128, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39989760).

21688128 is an abundant number, since it is smaller than the sum of its proper divisors (58291392).

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

21688128 is a wasteful number, since it uses less digits than its factorization.

21688128 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 202 (or 186 counting only the distinct ones).

The product of its digits is 12288, while the sum is 36.

The square root of 21688128 is about 4657.0514276740. The cubic root of 21688128 is about 278.8735697250.

It can be divided in two parts, 2168 and 8128, that added together give a triangular number (10296 = T₁₄₃).

The spelling of 21688128 in words is "twenty-one million, six hundred eighty-eight thousand, one hundred twenty-eight".