21501794778 has 16 divisors (see below), whose sum is σ = 43331862816. Its totient is φ = 7112552720.

The previous prime is 21501794687. The next prime is 21501794807. The reversal of 21501794778 is 87749710512.

It is a Smith number, since the sum of its digits (51) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21501794778.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13677201 + ... + 13678772.

It is an arithmetic number, because the mean of its divisors is an integer number (2708241426).

Almost surely, 2^21501794778 is an apocalyptic number.

21501794778 is an abundant number, since it is smaller than the sum of its proper divisors (21830068038).

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

21501794778 is a wasteful number, since it uses less digits than its factorization.

21501794778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27356109.

The product of its (nonzero) digits is 987840, while the sum is 51.

The spelling of 21501794778 in words is "twenty-one billion, five hundred one million, seven hundred ninety-four thousand, seven hundred seventy-eight".