21305689 has 2 divisors, whose sum is σ = 21305690. Its totient is φ = 21305688.

The previous prime is 21305681. The next prime is 21305699. The reversal of 21305689 is 98650312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15015625 + 6290064 = 3875^2 + 2508^2 .

It is a cyclic number.

It is not a de Polignac number, because 21305689 - 2³ = 21305681 is a prime.

It is not a weakly prime, because it can be changed into another prime (21305681) 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 as a sum of consecutive naturals, namely, 10652844 + 10652845.

It is an arithmetic number, because the mean of its divisors is an integer number (10652845).

Almost surely, 2^21305689 is an apocalyptic number.

It is an amenable number.

21305689 is a deficient number, since it is larger than the sum of its proper divisors (1).

21305689 is an equidigital number, since it uses as much as digits as its factorization.

21305689 is an odious number, because the sum of its binary digits is odd.

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

The square root of 21305689 is about 4615.8085965516. The cubic root of 21305689 is about 277.2246610189.

The spelling of 21305689 in words is "twenty-one million, three hundred five thousand, six hundred eighty-nine".