21540879666 has 160 divisors (see below), whose sum is σ = 51812006400. Its totient is φ = 6674088960.

The previous prime is 21540879649. The next prime is 21540879719. The reversal of 21540879666 is 66697804512.

It is a Smith number, since the sum of its digits (54) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is an unprimeable number.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 51410005 + ... + 51410423.

It is an arithmetic number, because the mean of its divisors is an integer number (323825040).

Almost surely, 2^21540879666 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21540879666, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25906003200).

21540879666 is an abundant number, since it is smaller than the sum of its proper divisors (30271126734).

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

21540879666 is a wasteful number, since it uses less digits than its factorization.

21540879666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 846 (or 837 counting only the distinct ones).

The product of its (nonzero) digits is 4354560, while the sum is 54.

The spelling of 21540879666 in words is "twenty-one billion, five hundred forty million, eight hundred seventy-nine thousand, six hundred sixty-six".