21818101 has 4 divisors (see below), whose sum is σ = 21856492. Its totient is φ = 21779712.

The previous prime is 21818077. The next prime is 21818117. The reversal of 21818101 is 10181812.

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 10080625 + 11737476 = 3175^2 + 3426^2 .

It is a cyclic number.

It is not a de Polignac number, because 21818101 - 2⁷ = 21817973 is a prime.

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 (21818171) 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, 18330 + ... + 19483.

It is an arithmetic number, because the mean of its divisors is an integer number (5464123).

Almost surely, 2^21818101 is an apocalyptic number.

It is an amenable number.

21818101 is a deficient number, since it is larger than the sum of its proper divisors (38391).

21818101 is an equidigital number, since it uses as much as digits as its factorization.

21818101 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 38390.

The product of its (nonzero) digits is 128, while the sum is 22.

The square root of 21818101 is about 4670.9850138916. The cubic root of 21818101 is about 279.4295400895.

Adding to 21818101 its reverse (10181812), we get a palindrome (31999913).

The spelling of 21818101 in words is "twenty-one million, eight hundred eighteen thousand, one hundred one".