21541209 has 8 divisors (see below), whose sum is σ = 28791840. Its totient is φ = 14325696.

The previous prime is 21541183. The next prime is 21541211. The reversal of 21541209 is 90214512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a de Polignac number, because none of the positive numbers 2^k-21541209 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21541259) 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 7 ways as a sum of consecutive naturals, for example, 7312 + ... + 9825.

It is an arithmetic number, because the mean of its divisors is an integer number (3598980).

Almost surely, 2^21541209 is an apocalyptic number.

It is an amenable number.

21541209 is a deficient number, since it is larger than the sum of its proper divisors (7250631).

21541209 is a wasteful number, since it uses less digits than its factorization.

21541209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17559.

The product of its (nonzero) digits is 720, while the sum is 24.

The square root of 21541209 is about 4641.2508012388. The cubic root of 21541209 is about 278.2424303844.

The spelling of 21541209 in words is "twenty-one million, five hundred forty-one thousand, two hundred nine".