21785251968 has 160 divisors (see below), whose sum is σ = 65563789500. Its totient is φ = 7179853824.

The previous prime is 21785251949. The next prime is 21785251979. The reversal of 21785251968 is 86915258712.

21785251968 is a `hidden beast` number, since 2 + 1 + 78 + 52 + 519 + 6 + 8 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 19090396224 + 2694855744 = 138168^2 + 51912^2 .

It is a super-3 number, since 3×21785251968³ (a number of 32 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 910948 + ... + 934556.

Almost surely, 2^21785251968 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 21785251968, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32781894750).

21785251968 is an abundant number, since it is smaller than the sum of its proper divisors (43778537532).

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

21785251968 is an equidigital number, since it uses as much as digits as its factorization.

21785251968 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23724 (or 23703 counting only the distinct ones).

The product of its digits is 2419200, while the sum is 54.

The spelling of 21785251968 in words is "twenty-one billion, seven hundred eighty-five million, two hundred fifty-one thousand, nine hundred sixty-eight".