21308738928666 has 192 divisors, whose sum is σ = 54801346314240. Its totient is φ = 5478198781440.

The previous prime is 21308738928599. The next prime is 21308738928691. The reversal of 21308738928666 is 66682983780312.

It is a Harshad number since it is a multiple of its sum of digits (69).

It is a self number, because there is not a number n which added to its sum of digits gives 21308738928666.

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 95 ways as a sum of consecutive naturals, for example, 234345751 + ... + 234436661.

It is an arithmetic number, because the mean of its divisors is an integer number (285423678720).

Almost surely, 2^{21308738928666} is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21308738928666, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27400673157120).

21308738928666 is an abundant number, since it is smaller than the sum of its proper divisors (33492607385574).

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

21308738928666 is a wasteful number, since it uses less digits than its factorization.

21308738928666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 93009 (or 93002 counting only the distinct ones).

The product of its (nonzero) digits is 250822656, while the sum is 69.

The spelling of 21308738928666 in words is "twenty-one trillion, three hundred eight billion, seven hundred thirty-eight million, nine hundred twenty-eight thousand, six hundred sixty-six".