21308266728 has 256 divisors, whose sum is σ = 69452697600. Its totient is φ = 5927489280.

The previous prime is 21308266723. The next prime is 21308266729. The reversal of 21308266728 is 82766280312.

It is not an unprimeable number, because it can be changed into a prime (21308266723) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 9498775 + ... + 9501017.

It is an arithmetic number, because the mean of its divisors is an integer number (271299600).

Almost surely, 2^21308266728 is an apocalyptic number.

21308266728 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21308266728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34726348800).

21308266728 is an abundant number, since it is smaller than the sum of its proper divisors (48144430872).

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

21308266728 is a wasteful number, since it uses less digits than its factorization.

21308266728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2429 (or 2419 counting only the distinct ones).

The product of its (nonzero) digits is 387072, while the sum is 45.

The spelling of 21308266728 in words is "twenty-one billion, three hundred eight million, two hundred sixty-six thousand, seven hundred twenty-eight".