21180155 has 16 divisors (see below), whose sum is σ = 27004320. Its totient is φ = 15902208.

The previous prime is 21180151. The next prime is 21180163. The reversal of 21180155 is 55108112.

It is a cyclic number.

It is not a de Polignac number, because 21180155 - 2² = 21180151 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21180155.

It is not an unprimeable number, because it can be changed into a prime (21180151) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9749 + ... + 11721.

It is an arithmetic number, because the mean of its divisors is an integer number (1687770).

Almost surely, 2^21180155 is an apocalyptic number.

21180155 is a deficient number, since it is larger than the sum of its proper divisors (5824165).

21180155 is a wasteful number, since it uses less digits than its factorization.

21180155 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2110.

The product of its (nonzero) digits is 400, while the sum is 23.

The square root of 21180155 is about 4602.1902394403. The cubic root of 21180155 is about 276.6791150993.

Adding to 21180155 its reverse (55108112), we get a palindrome (76288267).

The spelling of 21180155 in words is "twenty-one million, one hundred eighty thousand, one hundred fifty-five".