21020005 has 4 divisors (see below), whose sum is σ = 25224012. Its totient is φ = 16816000.

The previous prime is 21019993. The next prime is 21020011. The reversal of 21020005 is 50002012.

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 6874884 + 14145121 = 2622^2 + 3761^2 .

It is not a de Polignac number, because 21020005 - 2¹⁵ = 20987237 is a prime.

It is a super-2 number, since 2×21020005² = 883681220400050, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21019973 and 21020000.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2101996 + ... + 2102005.

It is an arithmetic number, because the mean of its divisors is an integer number (6306003).

Almost surely, 2^21020005 is an apocalyptic number.

It is an amenable number.

21020005 is a deficient number, since it is larger than the sum of its proper divisors (4204007).

21020005 is an equidigital number, since it uses as much as digits as its factorization.

21020005 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4204006.

The product of its (nonzero) digits is 20, while the sum is 10.

The square root of 21020005 is about 4584.7578998242. The cubic root of 21020005 is about 275.9799966249.

Adding to 21020005 its reverse (50002012), we get a palindrome (71022017).

The spelling of 21020005 in words is "twenty-one million, twenty thousand, five".