21109409 has 2 divisors, whose sum is σ = 21109410. Its totient is φ = 21109408.

The previous prime is 21109397. The next prime is 21109441. The reversal of 21109409 is 90490112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12229009 + 8880400 = 3497^2 + 2980^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21109409 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21102409) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10554704 + 10554705.

It is an arithmetic number, because the mean of its divisors is an integer number (10554705).

Almost surely, 2^21109409 is an apocalyptic number.

It is an amenable number.

21109409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21109409 is an equidigital number, since it uses as much as digits as its factorization.

21109409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 648, while the sum is 26.

The square root of 21109409 is about 4594.4976874518. The cubic root of 21109409 is about 276.3707167448.

The spelling of 21109409 in words is "twenty-one million, one hundred nine thousand, four hundred nine".