21318555 has 16 divisors (see below), whose sum is σ = 34578720. Its totient is φ = 11213568.

The previous prime is 21318541. The next prime is 21318599. The reversal of 21318555 is 55581312.

It is not a de Polignac number, because 21318555 - 2⁸ = 21318299 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, 8640 + ... + 10829.

It is an arithmetic number, because the mean of its divisors is an integer number (2161170).

Almost surely, 2^21318555 is an apocalyptic number.

21318555 is a deficient number, since it is larger than the sum of its proper divisors (13260165).

21318555 is a wasteful number, since it uses less digits than its factorization.

21318555 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19550.

The product of its digits is 6000, while the sum is 30.

The square root of 21318555 is about 4617.2020748501. The cubic root of 21318555 is about 277.2804529213.

Adding to 21318555 its reverse (55581312), we get a palindrome (76899867).

The spelling of 21318555 in words is "twenty-one million, three hundred eighteen thousand, five hundred fifty-five".