20561554944 has 640 divisors, whose sum is σ = 76366540800. Its totient is φ = 5326110720.

The previous prime is 20561554939. The next prime is 20561554963. The reversal of 20561554944 is 44945516502.

20561554944 is a `hidden beast` number, since 2 + 0 + 5 + 6 + 1 + 554 + 94 + 4 = 666.

It is a self number, because there is not a number n which added to its sum of digits gives 20561554944.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 47706409 + ... + 47706839.

It is an arithmetic number, because the mean of its divisors is an integer number (119322720).

Almost surely, 2^20561554944 is an apocalyptic number.

20561554944 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 20561554944, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38183270400).

20561554944 is an abundant number, since it is smaller than the sum of its proper divisors (55804985856).

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

20561554944 is a wasteful number, since it uses less digits than its factorization.

20561554944 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 511 (or 489 counting only the distinct ones).

The product of its (nonzero) digits is 864000, while the sum is 45.

The spelling of 20561554944 in words is "twenty billion, five hundred sixty-one million, five hundred fifty-four thousand, nine hundred forty-four".