21210005 has 16 divisors (see below), whose sum is σ = 26074224. Its totient is φ = 16558080.

The previous prime is 21209963. The next prime is 21210011. The reversal of 21210005 is 50001212.

It can be written as a sum of positive squares in 8 ways, for example, as 206116 + 21003889 = 454^2 + 4583^2 .

It is not a de Polignac number, because 21210005 - 2¹⁰ = 21208981 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 59909 + ... + 60261.

It is an arithmetic number, because the mean of its divisors is an integer number (1629639).

Almost surely, 2^21210005 is an apocalyptic number.

It is an amenable number.

21210005 is a deficient number, since it is larger than the sum of its proper divisors (4864219).

21210005 is a wasteful number, since it uses less digits than its factorization.

21210005 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 616.

The product of its (nonzero) digits is 20, while the sum is 11.

The square root of 21210005 is about 4605.4321187050. The cubic root of 21210005 is about 276.8090322281.

Adding to 21210005 its reverse (50001212), we get a palindrome (71211217).

The spelling of 21210005 in words is "twenty-one million, two hundred ten thousand, five".