21020305 has 4 divisors (see below), whose sum is σ = 25224372. Its totient is φ = 16816240.

The previous prime is 21020303. The next prime is 21020339. The reversal of 21020305 is 50302012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9884736 + 11135569 = 3144^2 + 3337^2 .

It is not a de Polignac number, because 21020305 - 2¹ = 21020303 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21020303) 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 in 3 ways as a sum of consecutive naturals, for example, 2102026 + ... + 2102035.

It is an arithmetic number, because the mean of its divisors is an integer number (6306093).

Almost surely, 2^21020305 is an apocalyptic number.

It is an amenable number.

21020305 is a deficient number, since it is larger than the sum of its proper divisors (4204067).

21020305 is an equidigital number, since it uses as much as digits as its factorization.

21020305 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4204066.

The product of its (nonzero) digits is 60, while the sum is 13.

The square root of 21020305 is about 4584.7906168112. The cubic root of 21020305 is about 275.9813095584.

Adding to 21020305 its reverse (50302012), we get a palindrome (71322317).

The spelling of 21020305 in words is "twenty-one million, twenty thousand, three hundred five".