21155181 has 16 divisors (see below), whose sum is σ = 29588160. Its totient is φ = 13426560.

The previous prime is 21155179. The next prime is 21155201. The reversal of 21155181 is 18155112.

It is not a de Polignac number, because 21155181 - 2¹ = 21155179 is a prime.

It is a super-2 number, since 2×21155181² = 895083366285522, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21155131) by changing a digit.

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, 4686 + ... + 8016.

It is an arithmetic number, because the mean of its divisors is an integer number (1849260).

Almost surely, 2^21155181 is an apocalyptic number.

It is an amenable number.

21155181 is a deficient number, since it is larger than the sum of its proper divisors (8432979).

21155181 is a wasteful number, since it uses less digits than its factorization.

21155181 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3436.

The product of its digits is 400, while the sum is 24.

The square root of 21155181 is about 4599.4761658258. The cubic root of 21155181 is about 276.5703261279.

The spelling of 21155181 in words is "twenty-one million, one hundred fifty-five thousand, one hundred eighty-one".