21456909 has 24 divisors (see below), whose sum is σ = 32853600. Its totient is φ = 13456800.

The previous prime is 21456901. The next prime is 21456913. The reversal of 21456909 is 90965412.

It is not a de Polignac number, because 21456909 - 2³ = 21456901 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a nialpdrome in base 9.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21456901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 30259 + ... + 30959.

It is an arithmetic number, because the mean of its divisors is an integer number (1368900).

Almost surely, 2^21456909 is an apocalyptic number.

It is an amenable number.

21456909 is a deficient number, since it is larger than the sum of its proper divisors (11396691).

21456909 is a wasteful number, since it uses less digits than its factorization.

21456909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 905 (or 902 counting only the distinct ones).

The product of its (nonzero) digits is 19440, while the sum is 36.

The square root of 21456909 is about 4632.1602951539. The cubic root of 21456909 is about 277.8789951788.

The spelling of 21456909 in words is "twenty-one million, four hundred fifty-six thousand, nine hundred nine".