21918081 has 4 divisors (see below), whose sum is σ = 29224112. Its totient is φ = 14612052.

The previous prime is 21918079. The next prime is 21918101. The reversal of 21918081 is 18081912.

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 not a de Polignac number, because 21918081 - 2¹ = 21918079 is a prime.

It is a super-2 number, since 2×21918081² = 960804549445122, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21918181) 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, 3653011 + ... + 3653016.

It is an arithmetic number, because the mean of its divisors is an integer number (7306028).

Almost surely, 2^21918081 is an apocalyptic number.

It is an amenable number.

21918081 is a deficient number, since it is larger than the sum of its proper divisors (7306031).

21918081 is an equidigital number, since it uses as much as digits as its factorization.

21918081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7306030.

The product of its (nonzero) digits is 1152, while the sum is 30.

The square root of 21918081 is about 4681.6750207591. The cubic root of 21918081 is about 279.8557122240.

Adding to 21918081 its reverse (18081912), we get a palindrome (39999993).

The spelling of 21918081 in words is "twenty-one million, nine hundred eighteen thousand, eighty-one".