21210057666 has 96 divisors (see below), whose sum is σ = 53104896000. Its totient is φ = 5992753248.

The previous prime is 21210057619. The next prime is 21210057689. The reversal of 21210057666 is 66675001212.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 21210057666.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 10609335 + ... + 10611333.

It is an arithmetic number, because the mean of its divisors is an integer number (553176000).

Almost surely, 2^21210057666 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21210057666, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26552448000).

21210057666 is an abundant number, since it is smaller than the sum of its proper divisors (31894838334).

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

21210057666 is a wasteful number, since it uses less digits than its factorization.

21210057666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2908 (or 2905 counting only the distinct ones).

The product of its (nonzero) digits is 30240, while the sum is 36.

Adding to 21210057666 its reverse (66675001212), we get a palindrome (87885058878).

The spelling of 21210057666 in words is "twenty-one billion, two hundred ten million, fifty-seven thousand, six hundred sixty-six".