21979728 has 80 divisors (see below), whose sum is σ = 63954240. Its totient is φ = 7226496.

The previous prime is 21979717. The next prime is 21979733. The reversal of 21979728 is 82797912.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 35550 + ... + 36162.

It is an arithmetic number, because the mean of its divisors is an integer number (799428).

Almost surely, 2^21979728 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 21979728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31977120).

21979728 is an abundant number, since it is smaller than the sum of its proper divisors (41974512).

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

21979728 is a wasteful number, since it uses less digits than its factorization.

21979728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 713 (or 701 counting only the distinct ones).

The product of its digits is 127008, while the sum is 45.

The square root of 21979728 is about 4688.2542593166. The cubic root of 21979728 is about 280.1178415544.

The spelling of 21979728 in words is "twenty-one million, nine hundred seventy-nine thousand, seven hundred twenty-eight".