21218155 has 16 divisors (see below), whose sum is σ = 30631680. Its totient is φ = 13783392.

The previous prime is 21218143. The next prime is 21218161. The reversal of 21218155 is 55181212.

It is not a de Polignac number, because 21218155 - 2¹³ = 21209963 is a prime.

It is an unprimeable number.

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, 15289 + ... + 16618.

It is an arithmetic number, because the mean of its divisors is an integer number (1914480).

Almost surely, 2^21218155 is an apocalyptic number.

21218155 is a deficient number, since it is larger than the sum of its proper divisors (9413525).

21218155 is a wasteful number, since it uses less digits than its factorization.

21218155 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 31938.

The product of its digits is 800, while the sum is 25.

The square root of 21218155 is about 4606.3168584022. The cubic root of 21218155 is about 276.8444825532.

Adding to 21218155 its reverse (55181212), we get a palindrome (76399367).

The spelling of 21218155 in words is "twenty-one million, two hundred eighteen thousand, one hundred fifty-five".