21358609 has 2 divisors, whose sum is σ = 21358610. Its totient is φ = 21358608.

The previous prime is 21358607. The next prime is 21358619. The reversal of 21358609 is 90685312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20277009 + 1081600 = 4503^2 + 1040^2 .

It is a cyclic number.

It is not a de Polignac number, because 21358609 - 2¹ = 21358607 is a prime.

Together with 21358607, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21358607) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10679304 + 10679305.

It is an arithmetic number, because the mean of its divisors is an integer number (10679305).

Almost surely, 2^21358609 is an apocalyptic number.

It is an amenable number.

21358609 is a deficient number, since it is larger than the sum of its proper divisors (1).

21358609 is an equidigital number, since it uses as much as digits as its factorization.

21358609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 12960, while the sum is 34.

The square root of 21358609 is about 4621.5375147239. The cubic root of 21358609 is about 277.4539988137.

The spelling of 21358609 in words is "twenty-one million, three hundred fifty-eight thousand, six hundred nine".