21687728 has 10 divisors (see below), whose sum is σ = 42020004. Its totient is φ = 10843856.

The previous prime is 21687719. The next prime is 21687749. The reversal of 21687728 is 82778612.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 677726 + ... + 677757.

Almost surely, 2^21687728 is an apocalyptic number.

It is an amenable number.

21687728 is a deficient number, since it is larger than the sum of its proper divisors (20332276).

21687728 is a wasteful number, since it uses less digits than its factorization.

21687728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1355491 (or 1355485 counting only the distinct ones).

The product of its digits is 75264, while the sum is 41.

The square root of 21687728 is about 4657.0084818475. The cubic root of 21687728 is about 278.8718552676.

The spelling of 21687728 in words is "twenty-one million, six hundred eighty-seven thousand, seven hundred twenty-eight".