21561328 has 20 divisors (see below), whose sum is σ = 41847520. Its totient is φ = 10761984.

The previous prime is 21561313. The next prime is 21561329. The reversal of 21561328 is 82316512.

It is a junction number, because it is equal to n+sod(n) for n = 21561296 and 21561305.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21561329) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 15976 + ... + 17272.

It is an arithmetic number, because the mean of its divisors is an integer number (2092376).

Almost surely, 2^21561328 is an apocalyptic number.

It is an amenable number.

21561328 is a deficient number, since it is larger than the sum of its proper divisors (20286192).

21561328 is a wasteful number, since it uses less digits than its factorization.

21561328 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2344 (or 2338 counting only the distinct ones).

The product of its digits is 2880, while the sum is 28.

The square root of 21561328 is about 4643.4177068190. The cubic root of 21561328 is about 278.3290274671.

The spelling of 21561328 in words is "twenty-one million, five hundred sixty-one thousand, three hundred twenty-eight".