21670665816 has 128 divisors (see below), whose sum is σ = 59417487360. Its totient is φ = 6556723200.

The previous prime is 21670665787. The next prime is 21670665857. The reversal of 21670665816 is 61856607612.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 3880146 + ... + 3885726.

It is an arithmetic number, because the mean of its divisors is an integer number (464199120).

Almost surely, 2^21670665816 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21670665816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29708743680).

21670665816 is an abundant number, since it is smaller than the sum of its proper divisors (37746821544).

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

21670665816 is a wasteful number, since it uses less digits than its factorization.

21670665816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5945 (or 5941 counting only the distinct ones).

The product of its (nonzero) digits is 725760, while the sum is 48.

The spelling of 21670665816 in words is "twenty-one billion, six hundred seventy million, six hundred sixty-five thousand, eight hundred sixteen".