21858181 has 4 divisors (see below), whose sum is σ = 21881664. Its totient is φ = 21834700.

The previous prime is 21858163. The next prime is 21858197. The reversal of 21858181 is 18185812.

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 21858181 - 2⁹ = 21857669 is a prime.

It is a super-2 number, since 2×21858181² = 955560153257522, which contains 22 as substring.

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 (21858581) 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, 10285 + ... + 12226.

It is an arithmetic number, because the mean of its divisors is an integer number (5470416).

Almost surely, 2^21858181 is an apocalyptic number.

It is an amenable number.

21858181 is a deficient number, since it is larger than the sum of its proper divisors (23483).

21858181 is an equidigital number, since it uses as much as digits as its factorization.

21858181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23482.

The product of its digits is 5120, while the sum is 34.

The square root of 21858181 is about 4675.2733609918. The cubic root of 21858181 is about 279.6005400784.

The spelling of 21858181 in words is "twenty-one million, eight hundred fifty-eight thousand, one hundred eighty-one".