21438909 has 12 divisors (see below), whose sum is σ = 31626816. Its totient is φ = 13988232.

The previous prime is 21438881. The next prime is 21438913. The reversal of 21438909 is 90983412.

It is not a de Polignac number, because 21438909 - 2²⁰ = 20390333 is a prime.

It is a super-2 number, since 2×21438909² = 919253638220562, which contains 22 as substring.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21430909) 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 in 11 ways as a sum of consecutive naturals, for example, 24919 + ... + 25764.

It is an arithmetic number, because the mean of its divisors is an integer number (2635568).

Almost surely, 2^21438909 is an apocalyptic number.

It is an amenable number.

21438909 is a deficient number, since it is larger than the sum of its proper divisors (10187907).

21438909 is a wasteful number, since it uses less digits than its factorization.

21438909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50736 (or 50733 counting only the distinct ones).

The product of its (nonzero) digits is 15552, while the sum is 36.

The square root of 21438909 is about 4630.2169495608. The cubic root of 21438909 is about 277.8012700783.

The spelling of 21438909 in words is "twenty-one million, four hundred thirty-eight thousand, nine hundred nine".