21543905 has 4 divisors (see below), whose sum is σ = 25852692. Its totient is φ = 17235120.

The previous prime is 21543883. The next prime is 21543911. The reversal of 21543905 is 50934512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 4096576 + 17447329 = 2024^2 + 4177^2 .

It is not a de Polignac number, because 21543905 - 2¹⁴ = 21527521 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 2154386 + ... + 2154395.

It is an arithmetic number, because the mean of its divisors is an integer number (6463173).

Almost surely, 2^21543905 is an apocalyptic number.

It is an amenable number.

21543905 is a deficient number, since it is larger than the sum of its proper divisors (4308787).

21543905 is an equidigital number, since it uses as much as digits as its factorization.

21543905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4308786.

The product of its (nonzero) digits is 5400, while the sum is 29.

The square root of 21543905 is about 4641.5412310999. The cubic root of 21543905 is about 278.2540377537.

The spelling of 21543905 in words is "twenty-one million, five hundred forty-three thousand, nine hundred five".