21666109 has 16 divisors (see below), whose sum is σ = 23779008. Its totient is φ = 19660032.

The previous prime is 21666101. The next prime is 21666121. The reversal of 21666109 is 90166612.

It is a cyclic number.

It is not a de Polignac number, because 21666109 - 2³ = 21666101 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21666101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 78079 + ... + 78355.

It is an arithmetic number, because the mean of its divisors is an integer number (1486188).

Almost surely, 2^21666109 is an apocalyptic number.

It is an amenable number.

21666109 is a deficient number, since it is larger than the sum of its proper divisors (2112899).

21666109 is a wasteful number, since it uses less digits than its factorization.

21666109 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 444.

The product of its (nonzero) digits is 3888, while the sum is 31.

The square root of 21666109 is about 4654.6867778616. The cubic root of 21666109 is about 278.7791617557.

The spelling of 21666109 in words is "twenty-one million, six hundred sixty-six thousand, one hundred nine".