21605370864 has 360 divisors, whose sum is σ = 72251781840. Its totient is φ = 5542225920.

The previous prime is 21605370851. The next prime is 21605370923. The reversal of 21605370864 is 46807350612.

It is a Harshad number since it is a multiple of its sum of digits (42).

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 71 ways as a sum of consecutive naturals, for example, 25328262 + ... + 25329114.

It is an arithmetic number, because the mean of its divisors is an integer number (200699394).

Almost surely, 2^21605370864 is an apocalyptic number.

21605370864 is a gapful number since it is divisible by the number (24) 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 21605370864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36125890920).

21605370864 is an abundant number, since it is smaller than the sum of its proper divisors (50646410976).

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

21605370864 is a wasteful number, since it uses less digits than its factorization.

21605370864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 989 (or 965 counting only the distinct ones).

The product of its (nonzero) digits is 241920, while the sum is 42.

The spelling of 21605370864 in words is "twenty-one billion, six hundred five million, three hundred seventy thousand, eight hundred sixty-four".