21604109 has 2 divisors, whose sum is σ = 21604110. Its totient is φ = 21604108.

The previous prime is 21604091. The next prime is 21604139. The reversal of 21604109 is 90140612.

It is a happy number.

Together with previous prime (21604091) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20448484 + 1155625 = 4522^2 + 1075^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21604109 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21604139) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10802054 + 10802055.

It is an arithmetic number, because the mean of its divisors is an integer number (10802055).

Almost surely, 2^21604109 is an apocalyptic number.

It is an amenable number.

21604109 is a deficient number, since it is larger than the sum of its proper divisors (1).

21604109 is an equidigital number, since it uses as much as digits as its factorization.

21604109 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 432, while the sum is 23.

The square root of 21604109 is about 4648.0220524434. The cubic root of 21604109 is about 278.5129884235.

The spelling of 21604109 in words is "twenty-one million, six hundred four thousand, one hundred nine".