21166655 has 4 divisors (see below), whose sum is σ = 25399992. Its totient is φ = 16933320.

The previous prime is 21166643. The next prime is 21166679. The reversal of 21166655 is 55666112.

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

It is not a de Polignac number, because 21166655 - 2¹⁸ = 20904511 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2116661 + ... + 2116670.

It is an arithmetic number, because the mean of its divisors is an integer number (6349998).

Almost surely, 2^21166655 is an apocalyptic number.

21166655 is a deficient number, since it is larger than the sum of its proper divisors (4233337).

21166655 is an equidigital number, since it uses as much as digits as its factorization.

21166655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4233336.

The product of its digits is 10800, while the sum is 32.

The square root of 21166655 is about 4600.7233126977. The cubic root of 21166655 is about 276.6203185211.

It can be divided in two parts, 211 and 66655, that added together give a palindrome (66866).

The spelling of 21166655 in words is "twenty-one million, one hundred sixty-six thousand, six hundred fifty-five".