21991953867828 has 96 divisors (see below), whose sum is σ = 59093951078400. Its totient is φ = 6235377100416.

The previous prime is 21991953867797. The next prime is 21991953867833. The reversal of 21991953867828 is 82876835919912.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 25342218 + ... + 26195646.

It is an arithmetic number, because the mean of its divisors is an integer number (615561990400).

Almost surely, 2^{21991953867828} is an apocalyptic number.

21991953867828 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 21991953867828, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29546975539200).

21991953867828 is an abundant number, since it is smaller than the sum of its proper divisors (37101997210572).

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

21991953867828 is a wasteful number, since it uses less digits than its factorization.

21991953867828 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 855789 (or 855787 counting only the distinct ones).

The product of its digits is 940584960, while the sum is 78.

The spelling of 21991953867828 in words is "twenty-one trillion, nine hundred ninety-one billion, nine hundred fifty-three million, eight hundred sixty-seven thousand, eight hundred twenty-eight".