21205447 has 2 divisors, whose sum is σ = 21205448. Its totient is φ = 21205446.

The previous prime is 21205399. The next prime is 21205453. The reversal of 21205447 is 74450212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21205447 - 2¹⁹ = 20681159 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21505447) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10602723 + 10602724.

It is an arithmetic number, because the mean of its divisors is an integer number (10602724).

Almost surely, 2^21205447 is an apocalyptic number.

21205447 is a deficient number, since it is larger than the sum of its proper divisors (1).

21205447 is an equidigital number, since it uses as much as digits as its factorization.

21205447 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2240, while the sum is 25.

The square root of 21205447 is about 4604.9372417005. The cubic root of 21205447 is about 276.7892021847.

Adding to 21205447 its reverse (74450212), we get a palindrome (95655659).

The spelling of 21205447 in words is "twenty-one million, two hundred five thousand, four hundred forty-seven".