21506166 has 48 divisors (see below), whose sum is σ = 51936768. Its totient is φ = 6375600.

The previous prime is 21506159. The next prime is 21506167. The reversal of 21506166 is 66160512.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21506167) 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, 8151 + ... + 10461.

It is an arithmetic number, because the mean of its divisors is an integer number (1082016).

Almost surely, 2^21506166 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21506166, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25968384).

21506166 is an abundant number, since it is smaller than the sum of its proper divisors (30430602).

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

21506166 is a wasteful number, since it uses less digits than its factorization.

21506166 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2377 (or 2374 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 21506166 is about 4637.4740969627. The cubic root of 21506166 is about 278.0914679264.

Adding to 21506166 its reverse (66160512), we get a palindrome (87666678).

The spelling of 21506166 in words is "twenty-one million, five hundred six thousand, one hundred sixty-six".