21643378566865 has 16 divisors (see below), whose sum is σ = 28489686878016. Its totient is φ = 15653674094400.

The previous prime is 21643378566847. The next prime is 21643378566877. The reversal of 21643378566865 is 56866587334612.

It is not a de Polignac number, because 21643378566865 - 2⁵ = 21643378566833 is a prime.

It is a super-2 number, since 2×21643378566865² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21643378566794 and 21643378566803.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1087050747 + ... + 1087070656.

It is an arithmetic number, because the mean of its divisors is an integer number (1780605429876).

Almost surely, 2^{21643378566865} is an apocalyptic number.

It is an amenable number.

21643378566865 is a deficient number, since it is larger than the sum of its proper divisors (6846308311151).

21643378566865 is a wasteful number, since it uses less digits than its factorization.

21643378566865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2174121600.

The product of its digits is 1045094400, while the sum is 70.

The spelling of 21643378566865 in words is "twenty-one trillion, six hundred forty-three billion, three hundred seventy-eight million, five hundred sixty-six thousand, eight hundred sixty-five".