21541809 has 8 divisors (see below), whose sum is σ = 29712960. Its totient is φ = 13865936.

The previous prime is 21541781. The next prime is 21541829. The reversal of 21541809 is 90814512.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21541809 - 2⁹ = 21541297 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21541829) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 123717 + ... + 123890.

It is an arithmetic number, because the mean of its divisors is an integer number (3714120).

Almost surely, 2^21541809 is an apocalyptic number.

21541809 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

21541809 is a deficient number, since it is larger than the sum of its proper divisors (8171151).

21541809 is a wasteful number, since it uses less digits than its factorization.

21541809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 247639.

The product of its (nonzero) digits is 2880, while the sum is 30.

The square root of 21541809 is about 4641.3154385368. The cubic root of 21541809 is about 278.2450137106.

It can be divided in two parts, 215 and 41809, that added together give a palindrome (42024).

The spelling of 21541809 in words is "twenty-one million, five hundred forty-one thousand, eight hundred nine".