21158817728 has 56 divisors (see below), whose sum is σ = 43116959232. Its totient is φ = 10297857024.

The previous prime is 21158817697. The next prime is 21158817737. The reversal of 21158817728 is 82771885112.

It is a happy number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 406226 + ... + 455342.

Almost surely, 2^21158817728 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 21158817728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21558479616).

21158817728 is an abundant number, since it is smaller than the sum of its proper divisors (21958141504).

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

21158817728 is a wasteful number, since it uses less digits than its factorization.

21158817728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49309 (or 49299 counting only the distinct ones).

The product of its digits is 501760, while the sum is 50.

The spelling of 21158817728 in words is "twenty-one billion, one hundred fifty-eight million, eight hundred seventeen thousand, seven hundred twenty-eight".