21305965 has 4 divisors (see below), whose sum is σ = 25567164. Its totient is φ = 17044768.

The previous prime is 21305939. The next prime is 21305983. The reversal of 21305965 is 56950312.

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 10323369 + 10982596 = 3213^2 + 3314^2 .

It is a cyclic number.

It is not a de Polignac number, because 21305965 - 2¹¹ = 21303917 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent 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, 2130592 + ... + 2130601.

It is an arithmetic number, because the mean of its divisors is an integer number (6391791).

Almost surely, 2^21305965 is an apocalyptic number.

It is an amenable number.

21305965 is a deficient number, since it is larger than the sum of its proper divisors (4261199).

21305965 is an equidigital number, since it uses as much as digits as its factorization.

21305965 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4261198.

The product of its (nonzero) digits is 8100, while the sum is 31.

The square root of 21305965 is about 4615.8384937084. The cubic root of 21305965 is about 277.2258580963.

The spelling of 21305965 in words is "twenty-one million, three hundred five thousand, nine hundred sixty-five".