21239801856 has 864 divisors, whose sum is σ = 80884833120. Its totient is φ = 5518098432.

The previous prime is 21239801801. The next prime is 21239801857. The reversal of 21239801856 is 65810893212.

It is a tau number, because it is divible by the number of its divisors (864).

It is a super-2 number, since 2×21239801856² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21239801857) by changing a digit.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 317011935 + ... + 317012001.

It is an arithmetic number, because the mean of its divisors is an integer number (93616705).

Almost surely, 2^21239801856 is an apocalyptic number.

21239801856 is a gapful number since it is divisible by the number (26) 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 21239801856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40442416560).

21239801856 is an abundant number, since it is smaller than the sum of its proper divisors (59645031264).

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

21239801856 is an equidigital number, since it uses as much as digits as its factorization.

21239801856 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 131 (or 92 counting only the distinct ones).

The product of its (nonzero) digits is 207360, while the sum is 45.

The spelling of 21239801856 in words is "twenty-one billion, two hundred thirty-nine million, eight hundred one thousand, eight hundred fifty-six".