21961728 has 66 divisors (see below), whose sum is σ = 63440624. Its totient is φ = 7317504.

The previous prime is 21961727. The next prime is 21961741. The reversal of 21961728 is 82716912.

21961728 is a `hidden beast` number, since 2 + 19 + 617 + 28 = 666.

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

It is a junction number, because it is equal to n+sod(n) for n = 21961692 and 21961701.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21961721) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 8025 + ... + 10407.

Almost surely, 2^21961728 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 21961728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31720312).

21961728 is an abundant number, since it is smaller than the sum of its proper divisors (41478896).

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

21961728 is a wasteful number, since it uses less digits than its factorization.

21961728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2409 (or 2388 counting only the distinct ones).

The product of its digits is 12096, while the sum is 36.

The square root of 21961728 is about 4686.3341750242. The cubic root of 21961728 is about 280.0413544361.

The spelling of 21961728 in words is "twenty-one million, nine hundred sixty-one thousand, seven hundred twenty-eight".