21978260865 has 24 divisors (see below), whose sum is σ = 41558894208. Its totient is φ = 10656126240.

The previous prime is 21978260833. The next prime is 21978260879. The reversal of 21978260865 is 56806287912.

21978260865 is a `hidden beast` number, since 21 + 9 + 7 + 8 + 2 + 608 + 6 + 5 = 666.

It is not a de Polignac number, because 21978260865 - 2⁵ = 21978260833 is a prime.

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 23 ways as a sum of consecutive naturals, for example, 22199769 + ... + 22200758.

It is an arithmetic number, because the mean of its divisors is an integer number (1731620592).

Almost surely, 2^21978260865 is an apocalyptic number.

It is an amenable number.

21978260865 is a deficient number, since it is larger than the sum of its proper divisors (19580633343).

21978260865 is a wasteful number, since it uses less digits than its factorization.

21978260865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 44400549 (or 44400546 counting only the distinct ones).

The product of its (nonzero) digits is 2903040, while the sum is 54.

The spelling of 21978260865 in words is "twenty-one billion, nine hundred seventy-eight million, two hundred sixty thousand, eight hundred sixty-five".