20561664 has 72 divisors (see below), whose sum is σ = 56144592. Its totient is φ = 6676480.

The previous prime is 20561663. The next prime is 20561683. The reversal of 20561664 is 46616502.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20561663) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 31162 + ... + 31814.

It is an arithmetic number, because the mean of its divisors is an integer number (779786).

Almost surely, 2^20561664 is an apocalyptic number.

20561664 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 20561664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28072296).

20561664 is an abundant number, since it is smaller than the sum of its proper divisors (35582928).

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

20561664 is an equidigital number, since it uses as much as digits as its factorization.

20561664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 713 (or 699 counting only the distinct ones).

The product of its (nonzero) digits is 8640, while the sum is 30.

The square root of 20561664 is about 4534.4971055234. The cubic root of 20561664 is about 273.9593240629.

The spelling of 20561664 in words is "twenty million, five hundred sixty-one thousand, six hundred sixty-four".