21031909 has 2 divisors, whose sum is σ = 21031910. Its totient is φ = 21031908.

The previous prime is 21031883. The next prime is 21031973. The reversal of 21031909 is 90913012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13068225 + 7963684 = 3615^2 + 2822^2 .

It is a cyclic number.

It is not a de Polignac number, because 21031909 - 2⁷ = 21031781 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21031979) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10515954 + 10515955.

It is an arithmetic number, because the mean of its divisors is an integer number (10515955).

Almost surely, 2^21031909 is an apocalyptic number.

It is an amenable number.

21031909 is a deficient number, since it is larger than the sum of its proper divisors (1).

21031909 is an equidigital number, since it uses as much as digits as its factorization.

21031909 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 486, while the sum is 25.

The square root of 21031909 is about 4586.0559307536. The cubic root of 21031909 is about 276.0320842419.

The spelling of 21031909 in words is "twenty-one million, thirty-one thousand, nine hundred nine".