21604105 has 4 divisors (see below), whose sum is σ = 25924932. Its totient is φ = 17283280.

The previous prime is 21604091. The next prime is 21604109. The reversal of 21604105 is 50140612.

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 6827769 + 14776336 = 2613^2 + 3844^2 .

It is not a de Polignac number, because 21604105 - 2²¹ = 19506953 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21604109) 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, 2160406 + ... + 2160415.

It is an arithmetic number, because the mean of its divisors is an integer number (6481233).

Almost surely, 2^21604105 is an apocalyptic number.

It is an amenable number.

21604105 is a deficient number, since it is larger than the sum of its proper divisors (4320827).

21604105 is an equidigital number, since it uses as much as digits as its factorization.

21604105 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4320826.

The product of its (nonzero) digits is 240, while the sum is 19.

The square root of 21604105 is about 4648.0216221528. The cubic root of 21604105 is about 278.5129712346.

Adding to 21604105 its reverse (50140612), we get a palindrome (71744717).

The spelling of 21604105 in words is "twenty-one million, six hundred four thousand, one hundred five".