21840181 has 4 divisors (see below), whose sum is σ = 23825664. Its totient is φ = 19854700.

The previous prime is 21840157. The next prime is 21840193. The reversal of 21840181 is 18104812.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21840181 - 2⁵ = 21840149 is a prime.

It is a super-2 number, since 2×21840181² = 953987012225522, 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 (21840131) 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 3 ways as a sum of consecutive naturals, for example, 992725 + ... + 992746.

It is an arithmetic number, because the mean of its divisors is an integer number (5956416).

Almost surely, 2^21840181 is an apocalyptic number.

It is an amenable number.

21840181 is a deficient number, since it is larger than the sum of its proper divisors (1985483).

21840181 is a wasteful number, since it uses less digits than its factorization.

21840181 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1985482.

The product of its (nonzero) digits is 512, while the sum is 25.

The square root of 21840181 is about 4673.3479433913. The cubic root of 21840181 is about 279.5237695572.

Adding to 21840181 its reverse (18104812), we get a palindrome (39944993).

The spelling of 21840181 in words is "twenty-one million, eight hundred forty thousand, one hundred eighty-one".