21166660 has 48 divisors (see below), whose sum is σ = 46230912. Its totient is φ = 8134400.

The previous prime is 21166643. The next prime is 21166679. The reversal of 21166660 is 6666112.

It is a hoax number, since the sum of its digits (28) coincides with the sum of the digits of its distinct prime factors.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 67905 + ... + 68215.

It is an arithmetic number, because the mean of its divisors is an integer number (963144).

Almost surely, 2^21166660 is an apocalyptic number.

21166660 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 21166660, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23115456).

21166660 is an abundant number, since it is smaller than the sum of its proper divisors (25064252).

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

21166660 is a wasteful number, since it uses less digits than its factorization.

21166660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 444 (or 442 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 28.

The square root of 21166660 is about 4600.7238560905. The cubic root of 21166660 is about 276.6203403022.

The spelling of 21166660 in words is "twenty-one million, one hundred sixty-six thousand, six hundred sixty".