21781779984 has 150 divisors (see below), whose sum is σ = 65145755070. Its totient is φ = 7025978880.

The previous prime is 21781779961. The next prime is 21781779991. The reversal of 21781779984 is 48997718712.

It can be written as a sum of positive squares in only one way, i.e., 11240240400 + 10541539584 = 106020^2 + 102672^2 .

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 29 ways as a sum of consecutive naturals, for example, 1236712 + ... + 1254200.

Almost surely, 2^21781779984 is an apocalyptic number.

21781779984 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 21781779984, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32572877535).

21781779984 is an abundant number, since it is smaller than the sum of its proper divisors (43363975086).

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

21781779984 is a wasteful number, since it uses less digits than its factorization.

21781779984 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17571 (or 17525 counting only the distinct ones).

The product of its digits is 14224896, while the sum is 63.

The spelling of 21781779984 in words is "twenty-one billion, seven hundred eighty-one million, seven hundred seventy-nine thousand, nine hundred eighty-four".