20561991264 has 288 divisors, whose sum is σ = 62649490176. Its totient is φ = 6630750720.

The previous prime is 20561991259. The next prime is 20561991287. The reversal of 20561991264 is 46219916502.

20561991264 is a `hidden beast` number, since 2 + 0 + 5 + 619 + 9 + 1 + 26 + 4 = 666.

It is a tau number, because it is divible by the number of its divisors (288).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 31780189 + ... + 31780835.

It is an arithmetic number, because the mean of its divisors is an integer number (217532952).

Almost surely, 2^20561991264 is an apocalyptic number.

20561991264 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 20561991264, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31324745088).

20561991264 is an abundant number, since it is smaller than the sum of its proper divisors (42087498912).

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

20561991264 is an equidigital number, since it uses as much as digits as its factorization.

20561991264 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 800 (or 780 counting only the distinct ones).

The product of its (nonzero) digits is 233280, while the sum is 45.

The spelling of 20561991264 in words is "twenty billion, five hundred sixty-one million, nine hundred ninety-one thousand, two hundred sixty-four".