21001666560 has 456 divisors, whose sum is σ = 78894707760. Its totient is φ = 4756340736.

The previous prime is 21001666547. The next prime is 21001666561. The reversal of 21001666560 is 6566610012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001666561) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 192675786 + ... + 192675894.

It is an arithmetic number, because the mean of its divisors is an integer number (173014710).

Almost surely, 2^21001666560 is an apocalyptic number.

21001666560 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 21001666560, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39447353880).

21001666560 is an abundant number, since it is smaller than the sum of its proper divisors (57893041200).

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

21001666560 is an frugal number, since it uses more digits than its factorization.

21001666560 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 167 (or 126 counting only the distinct ones).

The product of its (nonzero) digits is 12960, while the sum is 33.

The spelling of 21001666560 in words is "twenty-one billion, one million, six hundred sixty-six thousand, five hundred sixty".