21697265664 has 144 divisors (see below), whose sum is σ = 64298435040. Its totient is φ = 7231242240.

The previous prime is 21697265659. The next prime is 21697265687. The reversal of 21697265664 is 46656279612.

21697265664 is a `hidden beast` number, since 2 + 1 + 6 + 9 + 72 + 6 + 566 + 4 = 666.

It is a tau number, because it is divible by the number of its divisors (144).

It is a Smith number, since the sum of its digits (54) coincides with the sum of the digits of its prime factors.

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

It is a self number, because there is not a number n which added to its sum of digits gives 21697265664.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3535879 + ... + 3542009.

It is an arithmetic number, because the mean of its divisors is an integer number (446516910).

Almost surely, 2^21697265664 is an apocalyptic number.

21697265664 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 21697265664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32149217520).

21697265664 is an abundant number, since it is smaller than the sum of its proper divisors (42601169376).

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

21697265664 is an frugal number, since it uses more digits than its factorization.

21697265664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6174 (or 6136 counting only the distinct ones).

The product of its digits is 6531840, while the sum is 54.

The spelling of 21697265664 in words is "twenty-one billion, six hundred ninety-seven million, two hundred sixty-five thousand, six hundred sixty-four".