20961664 has 32 divisors (see below), whose sum is σ = 43207200. Its totient is φ = 10117632.

The previous prime is 20961649. The next prime is 20961667. The reversal of 20961664 is 46616902.

It is a tau number, because it is divible by the number of its divisors (32).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20961667) 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 3 ways as a sum of consecutive naturals, for example, 889 + ... + 6535.

It is an arithmetic number, because the mean of its divisors is an integer number (1350225).

Almost surely, 2^20961664 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20961664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21603600).

20961664 is an abundant number, since it is smaller than the sum of its proper divisors (22245536).

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

20961664 is an equidigital number, since it uses as much as digits as its factorization.

20961664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5690 (or 5678 counting only the distinct ones).

The product of its (nonzero) digits is 15552, while the sum is 34.

The square root of 20961664 is about 4578.3909837409. The cubic root of 20961664 is about 275.7244326507.

The spelling of 20961664 in words is "twenty million, nine hundred sixty-one thousand, six hundred sixty-four".