21781858464 has 288 divisors, whose sum is σ = 67641013440. Its totient is φ = 6622027776.

The previous prime is 21781858391. The next prime is 21781858477. The reversal of 21781858464 is 46485818712.

21781858464 is a `hidden beast` number, since 2 + 178 + 1 + 8 + 5 + 8 + 464 = 666.

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

It is a self number, because there is not a number n which added to its sum of digits gives 21781858464.

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, 33052567 + ... + 33053225.

It is an arithmetic number, because the mean of its divisors is an integer number (234864630).

Almost surely, 2^21781858464 is an apocalyptic number.

21781858464 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 21781858464, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33820506720).

21781858464 is an abundant number, since it is smaller than the sum of its proper divisors (45859154976).

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

21781858464 is a wasteful number, since it uses less digits than its factorization.

21781858464 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 892 (or 881 counting only the distinct ones).

The product of its digits is 3440640, while the sum is 54.

The spelling of 21781858464 in words is "twenty-one billion, seven hundred eighty-one million, eight hundred fifty-eight thousand, four hundred sixty-four".