21305313 has 12 divisors (see below), whose sum is σ = 31296720. Its totient is φ = 13962456.

The previous prime is 21305309. The next prime is 21305321. The reversal of 21305313 is 31350312.

21305313 is a `hidden beast` number, since 2 + 130 + 531 + 3 = 666.

It is not a de Polignac number, because 21305313 - 2² = 21305309 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21305113) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 19531 + ... + 20592.

It is an arithmetic number, because the mean of its divisors is an integer number (2608060).

Almost surely, 2^21305313 is an apocalyptic number.

It is an amenable number.

21305313 is a deficient number, since it is larger than the sum of its proper divisors (9991407).

21305313 is a wasteful number, since it uses less digits than its factorization.

21305313 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40188 (or 40185 counting only the distinct ones).

The product of its (nonzero) digits is 270, while the sum is 18.

The square root of 21305313 is about 4615.7678667801. The cubic root of 21305313 is about 277.2230302012.

Adding to 21305313 its reverse (31350312), we get a palindrome (52655625).

The spelling of 21305313 in words is "twenty-one million, three hundred five thousand, three hundred thirteen".