21020002009 has 4 divisors (see below), whose sum is σ = 21307947316. Its totient is φ = 20732056704.

The previous prime is 21020002001. The next prime is 21020002063. The reversal of 21020002009 is 90020002012.

It is a happy number.

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 8367126784 + 12652875225 = 91472^2 + 112485^2 .

It is a cyclic number.

It is not a de Polignac number, because 21020002009 - 2³ = 21020002001 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21020001983 and 21020002001.

It is not an unprimeable number, because it can be changed into a prime (21020002001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 143972544 + ... + 143972689.

It is an arithmetic number, because the mean of its divisors is an integer number (5326986829).

Almost surely, 2^21020002009 is an apocalyptic number.

It is an amenable number.

21020002009 is a deficient number, since it is larger than the sum of its proper divisors (287945307).

21020002009 is an equidigital number, since it uses as much as digits as its factorization.

21020002009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 287945306.

The product of its (nonzero) digits is 72, while the sum is 16.

The spelling of 21020002009 in words is "twenty-one billion, twenty million, two thousand, nine".