21218185 has 8 divisors (see below), whose sum is σ = 25615296. Its totient is φ = 16872240.

The previous prime is 21218173. The next prime is 21218189. The reversal of 21218185 is 58181212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21218185 - 2⁹ = 21217673 is a prime.

It is a super-2 number, since 2×21218185² = 900422749388450, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21218189) 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, 11871 + ... + 13540.

It is an arithmetic number, because the mean of its divisors is an integer number (3201912).

Almost surely, 2^21218185 is an apocalyptic number.

It is an amenable number.

21218185 is a deficient number, since it is larger than the sum of its proper divisors (4397111).

21218185 is a wasteful number, since it uses less digits than its factorization.

21218185 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25583.

The product of its digits is 1280, while the sum is 28.

The square root of 21218185 is about 4606.3201147988. The cubic root of 21218185 is about 276.8446130284.

Adding to 21218185 its reverse (58181212), we get a palindrome (79399397).

The spelling of 21218185 in words is "twenty-one million, two hundred eighteen thousand, one hundred eighty-five".