21400205 has 4 divisors (see below), whose sum is σ = 25680252. Its totient is φ = 17120160.

The previous prime is 21400201. The next prime is 21400217. The reversal of 21400205 is 50200412.

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 4932841 + 16467364 = 2221^2 + 4058^2 .

It is not a de Polignac number, because 21400205 - 2² = 21400201 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21400205.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21400201) 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 3 ways as a sum of consecutive naturals, for example, 2140016 + ... + 2140025.

It is an arithmetic number, because the mean of its divisors is an integer number (6420063).

Almost surely, 2^21400205 is an apocalyptic number.

It is an amenable number.

21400205 is a deficient number, since it is larger than the sum of its proper divisors (4280047).

21400205 is an equidigital number, since it uses as much as digits as its factorization.

21400205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4280046.

The product of its (nonzero) digits is 80, while the sum is 14.

The square root of 21400205 is about 4626.0355597423. The cubic root of 21400205 is about 277.6339963749.

Adding to 21400205 its reverse (50200412), we get a palindrome (71600617).

The spelling of 21400205 in words is "twenty-one million, four hundred thousand, two hundred five".