21305203 has 2 divisors, whose sum is σ = 21305204. Its totient is φ = 21305202.

The previous prime is 21305191. The next prime is 21305209. The reversal of 21305203 is 30250312.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21305203 is a prime.

It is not a weakly prime, because it can be changed into another prime (21305209) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10652601 + 10652602.

It is an arithmetic number, because the mean of its divisors is an integer number (10652602).

Almost surely, 2^21305203 is an apocalyptic number.

21305203 is a deficient number, since it is larger than the sum of its proper divisors (1).

21305203 is an equidigital number, since it uses as much as digits as its factorization.

21305203 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 180, while the sum is 16.

The square root of 21305203 is about 4615.7559510875. The cubic root of 21305203 is about 277.2225530966. Note that the first 3 decimals are identical.

Adding to 21305203 its reverse (30250312), we get a palindrome (51555515).

The spelling of 21305203 in words is "twenty-one million, three hundred five thousand, two hundred three".