21202009 has 4 divisors (see below), whose sum is σ = 22449204. Its totient is φ = 19954816.

The previous prime is 21202003. The next prime is 21202033. The reversal of 21202009 is 90020212.

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 16040025 + 5161984 = 4005^2 + 2272^2 .

It is a cyclic number.

It is not a de Polignac number, because 21202009 - 2³ = 21202001 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21201983 and 21202001.

It is not an unprimeable number, because it can be changed into a prime (21202001) 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, 623572 + ... + 623605.

It is an arithmetic number, because the mean of its divisors is an integer number (5612301).

Almost surely, 2^21202009 is an apocalyptic number.

It is an amenable number.

21202009 is a deficient number, since it is larger than the sum of its proper divisors (1247195).

21202009 is a wasteful number, since it uses less digits than its factorization.

21202009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1247194.

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

The square root of 21202009 is about 4604.5639315792. The cubic root of 21202009 is about 276.7742429353.

The spelling of 21202009 in words is "twenty-one million, two hundred two thousand, nine".