21278556438815 has 16 divisors (see below), whose sum is σ = 27499219557600. Its totient is φ = 15712951300992.

The previous prime is 21278556438793. The next prime is 21278556438851. The reversal of 21278556438815 is 51883465587212.

It is a cyclic number.

It is not a de Polignac number, because 21278556438815 - 2⁶ = 21278556438751 is a prime.

It is a Smith number, since the sum of its digits (65) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Harshad number since it is a multiple of its sum of digits (65).

It is a congruent number.

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, 2301485 + ... + 6917654.

It is an arithmetic number, because the mean of its divisors is an integer number (1718701222350).

Almost surely, 2^{21278556438815} is an apocalyptic number.

21278556438815 is a deficient number, since it is larger than the sum of its proper divisors (6220663118785).

21278556438815 is a wasteful number, since it uses less digits than its factorization.

21278556438815 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9254666.

The product of its digits is 129024000, while the sum is 65.

The spelling of 21278556438815 in words is "twenty-one trillion, two hundred seventy-eight billion, five hundred fifty-six million, four hundred thirty-eight thousand, eight hundred fifteen".