21284728 has 8 divisors (see below), whose sum is σ = 39908880. Its totient is φ = 10642360.

The previous prime is 21284723. The next prime is 21284741. The reversal of 21284728 is 82748212.

It is a tau number, because it is divible by the number of its divisors (8).

It is a junction number, because it is equal to n+sod(n) for n = 21284693 and 21284702.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21284723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1330288 + ... + 1330303.

It is an arithmetic number, because the mean of its divisors is an integer number (4988610).

Almost surely, 2^21284728 is an apocalyptic number.

It is an amenable number.

21284728 is a deficient number, since it is larger than the sum of its proper divisors (18624152).

21284728 is a wasteful number, since it uses less digits than its factorization.

21284728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2660597 (or 2660593 counting only the distinct ones).

The product of its digits is 14336, while the sum is 34.

The square root of 21284728 is about 4613.5374713987. The cubic root of 21284728 is about 277.1337179724.

The spelling of 21284728 in words is "twenty-one million, two hundred eighty-four thousand, seven hundred twenty-eight".