21005166 has 128 divisors (see below), whose sum is σ = 57286656. Its totient is φ = 4976640.

The previous prime is 21005143. The next prime is 21005177. The reversal of 21005166 is 66150012.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (21).

21005166 is a modest number, since divided by 5166 gives 210 as remainder.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 287706 + ... + 287778.

It is an arithmetic number, because the mean of its divisors is an integer number (447552).

Almost surely, 2^21005166 is an apocalyptic number.

21005166 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 21005166, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28643328).

21005166 is an abundant number, since it is smaller than the sum of its proper divisors (36281490).

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

21005166 is a wasteful number, since it uses less digits than its factorization.

21005166 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 146.

The product of its (nonzero) digits is 360, while the sum is 21.

The square root of 21005166 is about 4583.1393171057. The cubic root of 21005166 is about 275.9150389615.

Adding to 21005166 its reverse (66150012), we get a palindrome (87155178).

The spelling of 21005166 in words is "twenty-one million, five thousand, one hundred sixty-six".