21155066660 has 96 divisors (see below), whose sum is σ = 54769236480. Its totient is φ = 6684023808.

The previous prime is 21155066657. The next prime is 21155066689. The reversal of 21155066660 is 6666055112.

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 31 ways as a sum of consecutive naturals, for example, 1113521 + ... + 1132359.

It is an arithmetic number, because the mean of its divisors is an integer number (570512880).

Almost surely, 2^21155066660 is an apocalyptic number.

21155066660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21155066660, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27384618240).

21155066660 is an abundant number, since it is smaller than the sum of its proper divisors (33614169820).

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

21155066660 is a wasteful number, since it uses less digits than its factorization.

21155066660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19485 (or 19483 counting only the distinct ones).

The product of its (nonzero) digits is 64800, while the sum is 38.

The spelling of 21155066660 in words is "twenty-one billion, one hundred fifty-five million, sixty-six thousand, six hundred sixty".