21200009 has 4 divisors (see below), whose sum is σ = 21267204. Its totient is φ = 21132816.

The previous prime is 21199999. The next prime is 21200021. The reversal of 21200009 is 90000212.

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 697225 + 20502784 = 835^2 + 4528^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21200009 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21199966 and 21200002.

It is not an unprimeable number, because it can be changed into a prime (21200209) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 33122 + ... + 33755.

It is an arithmetic number, because the mean of its divisors is an integer number (5316801).

Almost surely, 2^21200009 is an apocalyptic number.

It is an amenable number.

21200009 is a deficient number, since it is larger than the sum of its proper divisors (67195).

21200009 is an equidigital number, since it uses as much as digits as its factorization.

21200009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 67194.

The product of its (nonzero) digits is 36, while the sum is 14.

The square root of 21200009 is about 4604.3467506260. The cubic root of 21200009 is about 276.7655398938.

The spelling of 21200009 in words is "twenty-one million, two hundred thousand, nine".