21497591808 has 1008 divisors, whose sum is σ = 85721191920. Its totient is φ = 5255331840.

The previous prime is 21497591779. The next prime is 21497591821. The reversal of 21497591808 is 80819579412.

It is a happy number.

21497591808 is a `hidden beast` number, since 2 + 1 + 49 + 7 + 591 + 8 + 0 + 8 = 666.

It is a tau number, because it is divible by the number of its divisors (1008).

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 83 ways as a sum of consecutive naturals, for example, 1264564216 + ... + 1264564232.

It is an arithmetic number, because the mean of its divisors is an integer number (85040865).

Almost surely, 2^21497591808 is an apocalyptic number.

21497591808 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 21497591808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (42860595960).

21497591808 is an abundant number, since it is smaller than the sum of its proper divisors (64223600112).

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

21497591808 is an equidigital number, since it uses as much as digits as its factorization.

21497591808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 86 (or 40 counting only the distinct ones).

The product of its (nonzero) digits is 1451520, while the sum is 54.

It can be divided in two parts, 2149 and 7591808, that added together give a palindrome (7593957).

The spelling of 21497591808 in words is "twenty-one billion, four hundred ninety-seven million, five hundred ninety-one thousand, eight hundred eight".