21666111 has 4 divisors (see below), whose sum is σ = 28888152. Its totient is φ = 14444072.

The previous prime is 21666101. The next prime is 21666121. The reversal of 21666111 is 11166612.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21666101) and next prime (21666121).

It is a cyclic number.

It is not a de Polignac number, because 21666111 - 2¹⁰ = 21665087 is a prime.

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 polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3611016 + ... + 3611021.

It is an arithmetic number, because the mean of its divisors is an integer number (7222038).

Almost surely, 2^21666111 is an apocalyptic number.

21666111 is a deficient number, since it is larger than the sum of its proper divisors (7222041).

21666111 is an equidigital number, since it uses as much as digits as its factorization.

21666111 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7222040.

The product of its digits is 432, while the sum is 24.

The square root of 21666111 is about 4654.6869926989. The cubic root of 21666111 is about 278.7791703337.

It can be divided in two parts, 2166611 and 1, that added together give a palindrome (2166612).

The spelling of 21666111 in words is "twenty-one million, six hundred sixty-six thousand, one hundred eleven".