21638857408 has 224 divisors, whose sum is σ = 53569372160. Its totient is φ = 8465264640.

The previous prime is 21638857403. The next prime is 21638857459. The reversal of 21638857408 is 80475883612.

It is a tau number, because it is divible by the number of its divisors (224).

It is not an unprimeable number, because it can be changed into a prime (21638857403) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 39997618 + ... + 39998158.

Almost surely, 2^21638857408 is an apocalyptic number.

21638857408 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 21638857408, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26784686080).

21638857408 is an abundant number, since it is smaller than the sum of its proper divisors (31930514752).

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

21638857408 is a wasteful number, since it uses less digits than its factorization.

21638857408 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 743 (or 733 counting only the distinct ones).

The product of its (nonzero) digits is 2580480, while the sum is 52.

The spelling of 21638857408 in words is "twenty-one billion, six hundred thirty-eight million, eight hundred fifty-seven thousand, four hundred eight".