21852181 has 8 divisors (see below), whose sum is σ = 23569560. Its totient is φ = 20140032.

The previous prime is 21852169. The next prime is 21852197. The reversal of 21852181 is 18125812.

It can be written as a sum of positive squares in 4 ways, for example, as 378225 + 21473956 = 615^2 + 4634^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21852181 - 2¹⁹ = 21327893 is a prime.

It is a super-4 number, since 4×21852181⁴ (a number of 30 digits) contains 4444 as substring. Note that it is a super-d number also for d = 2.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21852121) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 14805 + ... + 16213.

It is an arithmetic number, because the mean of its divisors is an integer number (2946195).

Almost surely, 2^21852181 is an apocalyptic number.

It is an amenable number.

21852181 is a deficient number, since it is larger than the sum of its proper divisors (1717379).

21852181 is a wasteful number, since it uses less digits than its factorization.

21852181 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2615.

The product of its digits is 1280, while the sum is 28.

The square root of 21852181 is about 4674.6316432421. The cubic root of 21852181 is about 279.5749545891.

Adding to 21852181 its reverse (18125812), we get a palindrome (39977993).

The spelling of 21852181 in words is "twenty-one million, eight hundred fifty-two thousand, one hundred eighty-one".