21205465 has 4 divisors (see below), whose sum is σ = 25446564. Its totient is φ = 16964368.

The previous prime is 21205453. The next prime is 21205523. The reversal of 21205465 is 56450212.

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 7225344 + 13980121 = 2688^2 + 3739^2 .

It is a cyclic number.

It is not a de Polignac number, because 21205465 - 2¹⁷ = 21074393 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2120542 + ... + 2120551.

It is an arithmetic number, because the mean of its divisors is an integer number (6361641).

Almost surely, 2^21205465 is an apocalyptic number.

It is an amenable number.

21205465 is a deficient number, since it is larger than the sum of its proper divisors (4241099).

21205465 is an equidigital number, since it uses as much as digits as its factorization.

21205465 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4241098.

The product of its (nonzero) digits is 2400, while the sum is 25.

The square root of 21205465 is about 4604.9391961241. The cubic root of 21205465 is about 276.7892805011.

Adding to 21205465 its reverse (56450212), we get a palindrome (77655677).

The spelling of 21205465 in words is "twenty-one million, two hundred five thousand, four hundred sixty-five".