21728440 has 32 divisors (see below), whose sum is σ = 49124880. Its totient is φ = 8649472.

The previous prime is 21728437. The next prime is 21728467. The reversal of 21728440 is 4482712.

It is a junction number, because it is equal to n+sod(n) for n = 21728399 and 21728408.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7884 + ... + 10276.

Almost surely, 2^21728440 is an apocalyptic number.

21728440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21728440 is an abundant number, since it is smaller than the sum of its proper divisors (27396440).

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

21728440 is a wasteful number, since it uses less digits than its factorization.

21728440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2631 (or 2627 counting only the distinct ones).

The product of its (nonzero) digits is 3584, while the sum is 28.

The square root of 21728440 is about 4661.3774788146. The cubic root of 21728440 is about 279.0462447378.

The spelling of 21728440 in words is "twenty-one million, seven hundred twenty-eight thousand, four hundred forty".