21604091 has 2 divisors, whose sum is σ = 21604092. Its totient is φ = 21604090.

The previous prime is 21604081. The next prime is 21604109. The reversal of 21604091 is 19040612.

It is a happy number.

Together with next prime (21604109) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21604091 - 2⁶ = 21604027 is a prime.

It is a super-4 number, since 4×21604091⁴ (a number of 30 digits) contains 4444 as substring.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (21604021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10802045 + 10802046.

It is an arithmetic number, because the mean of its divisors is an integer number (10802046).

Almost surely, 2^21604091 is an apocalyptic number.

21604091 is a deficient number, since it is larger than the sum of its proper divisors (1).

21604091 is an equidigital number, since it uses as much as digits as its factorization.

21604091 is an odious number, because the sum of its binary digits is odd.

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

The square root of 21604091 is about 4648.0201161355. The cubic root of 21604091 is about 278.5129110735.

The spelling of 21604091 in words is "twenty-one million, six hundred four thousand, ninety-one".