21781585056 has 576 divisors, whose sum is σ = 77132611584. Its totient is φ = 5312563200.

The previous prime is 21781584991. The next prime is 21781585073. The reversal of 21781585056 is 65058518712.

It is a Harshad number since it is a multiple of its sum of digits (48).

It is a junction number, because it is equal to n+sod(n) for n = 21781584996 and 21781585014.

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 59350185 + ... + 59350551.

It is an arithmetic number, because the mean of its divisors is an integer number (133910784).

Almost surely, 2^21781585056 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 21781585056, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38566305792).

21781585056 is an abundant number, since it is smaller than the sum of its proper divisors (55351026528).

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

21781585056 is a wasteful number, since it uses less digits than its factorization.

21781585056 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 473 (or 458 counting only the distinct ones).

The product of its (nonzero) digits is 672000, while the sum is 48.

The spelling of 21781585056 in words is "twenty-one billion, seven hundred eighty-one million, five hundred eighty-five thousand, fifty-six".