21003666 has 16 divisors (see below), whose sum is σ = 42120000. Its totient is φ = 6982448.

The previous prime is 21003659. The next prime is 21003667. The reversal of 21003666 is 66630012.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21003667) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 2166 + ... + 6833.

It is an arithmetic number, because the mean of its divisors is an integer number (2632500).

Almost surely, 2^21003666 is an apocalyptic number.

21003666 is an abundant number, since it is smaller than the sum of its proper divisors (21116334).

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

21003666 is a wasteful number, since it uses less digits than its factorization.

21003666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9393.

The product of its (nonzero) digits is 1296, while the sum is 24.

The square root of 21003666 is about 4582.9756708933. The cubic root of 21003666 is about 275.9084710152.

Adding to 21003666 its reverse (66630012), we get a palindrome (87633678).

The spelling of 21003666 in words is "twenty-one million, three thousand, six hundred sixty-six".