21043409 has 2 divisors, whose sum is σ = 21043410. Its totient is φ = 21043408.

The previous prime is 21043391. The next prime is 21043423. The reversal of 21043409 is 90434012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20729809 + 313600 = 4553^2 + 560^2 .

It is a cyclic number.

It is not a de Polignac number, because 21043409 - 2⁸ = 21043153 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 (21043489) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10521704 + 10521705.

It is an arithmetic number, because the mean of its divisors is an integer number (10521705).

Almost surely, 2^21043409 is an apocalyptic number.

It is an amenable number.

21043409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21043409 is an equidigital number, since it uses as much as digits as its factorization.

21043409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 864, while the sum is 23.

The square root of 21043409 is about 4587.3095600799. The cubic root of 21043409 is about 276.0823854386.

The spelling of 21043409 in words is "twenty-one million, forty-three thousand, four hundred nine".