21202409 has 2 divisors, whose sum is σ = 21202410. Its totient is φ = 21202408.

The previous prime is 21202403. The next prime is 21202421. The reversal of 21202409 is 90420212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19114384 + 2088025 = 4372^2 + 1445^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21202409 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21202403) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10601204 + 10601205.

It is an arithmetic number, because the mean of its divisors is an integer number (10601205).

Almost surely, 2^21202409 is an apocalyptic number.

It is an amenable number.

21202409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21202409 is an equidigital number, since it uses as much as digits as its factorization.

21202409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 20.

The square root of 21202409 is about 4604.6073665406. The cubic root of 21202409 is about 276.7759834779.

The spelling of 21202409 in words is "twenty-one million, two hundred two thousand, four hundred nine".