21420205 has 4 divisors (see below), whose sum is σ = 25704252. Its totient is φ = 17136160.

The previous prime is 21420169. The next prime is 21420209. The reversal of 21420205 is 50202412.

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 8874441 + 12545764 = 2979^2 + 3542^2 .

It is not a de Polignac number, because 21420205 - 2¹¹ = 21418157 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21420209) 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 in 3 ways as a sum of consecutive naturals, for example, 2142016 + ... + 2142025.

It is an arithmetic number, because the mean of its divisors is an integer number (6426063).

Almost surely, 2^21420205 is an apocalyptic number.

It is an amenable number.

21420205 is a deficient number, since it is larger than the sum of its proper divisors (4284047).

21420205 is an equidigital number, since it uses as much as digits as its factorization.

21420205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4284046.

The product of its (nonzero) digits is 160, while the sum is 16.

The square root of 21420205 is about 4628.1967330700. The cubic root of 21420205 is about 277.7204589584.

Adding to 21420205 its reverse (50202412), we get a palindrome (71622617).

The spelling of 21420205 in words is "twenty-one million, four hundred twenty thousand, two hundred five".