21687328 has 48 divisors (see below), whose sum is σ = 47257560. Its totient is φ = 9732096.

The previous prime is 21687307. The next prime is 21687329. The reversal of 21687328 is 82378612.

It can be written as a sum of positive squares in 4 ways, for example, as 12759184 + 8928144 = 3572^2 + 2988^2 .

It is a Harshad number since it is a multiple of its sum of digits (37).

It is not an unprimeable number, because it can be changed into a prime (21687329) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 14688 + ... + 16096.

Almost surely, 2^21687328 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 21687328, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23628780).

21687328 is an abundant number, since it is smaller than the sum of its proper divisors (25570232).

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

21687328 is a wasteful number, since it uses less digits than its factorization.

21687328 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1469 (or 1461 counting only the distinct ones).

The product of its digits is 32256, while the sum is 37.

The square root of 21687328 is about 4656.9655356251. The cubic root of 21687328 is about 278.8701407892.

The spelling of 21687328 in words is "twenty-one million, six hundred eighty-seven thousand, three hundred twenty-eight".