21855181 has 4 divisors (see below), whose sum is σ = 21877372. Its totient is φ = 21832992.

The previous prime is 21855161. The next prime is 21855191. The reversal of 21855181 is 18155812.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 10692900 + 11162281 = 3270^2 + 3341^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21855181 is a prime.

It is a super-2 number, since 2×21855181² = 955297873085522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21855121) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9546 + ... + 11611.

It is an arithmetic number, because the mean of its divisors is an integer number (5469343).

Almost surely, 2^21855181 is an apocalyptic number.

It is an amenable number.

21855181 is a deficient number, since it is larger than the sum of its proper divisors (22191).

21855181 is a wasteful number, since it uses less digits than its factorization.

21855181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22190.

The product of its digits is 3200, while the sum is 31.

The square root of 21855181 is about 4674.9525131278. The cubic root of 21855181 is about 279.5877479191.

The spelling of 21855181 in words is "twenty-one million, eight hundred fifty-five thousand, one hundred eighty-one".