21540205 has 16 divisors (see below), whose sum is σ = 27846720. Its totient is φ = 15942528.

The previous prime is 21540203. The next prime is 21540209. The reversal of 21540205 is 50204512.

It is a cyclic number.

It is not a de Polignac number, because 21540205 - 2¹ = 21540203 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (19).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21540203) 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 15 ways as a sum of consecutive naturals, for example, 1449 + ... + 6721.

It is an arithmetic number, because the mean of its divisors is an integer number (1740420).

Almost surely, 2^21540205 is an apocalyptic number.

It is an amenable number.

21540205 is a deficient number, since it is larger than the sum of its proper divisors (6306515).

21540205 is a wasteful number, since it uses less digits than its factorization.

21540205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5340.

The product of its (nonzero) digits is 400, while the sum is 19.

The square root of 21540205 is about 4641.1426394801. The cubic root of 21540205 is about 278.2381075113.

Adding to 21540205 its reverse (50204512), we get a palindrome (71744717).

The spelling of 21540205 in words is "twenty-one million, five hundred forty thousand, two hundred five".