21665313 has 20 divisors (see below), whose sum is σ = 33243540. Its totient is φ = 14051232.

The previous prime is 21665279. The next prime is 21665341. The reversal of 21665313 is 31356612.

21665313 is a `hidden beast` number, since 2 + 1 + 6 + 653 + 1 + 3 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 20903184 + 762129 = 4572^2 + 873^2 .

It is not a de Polignac number, because 21665313 - 2⁹ = 21664801 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21665353) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 618 + ... + 6611.

It is an arithmetic number, because the mean of its divisors is an integer number (1662177).

Almost surely, 2^21665313 is an apocalyptic number.

It is an amenable number.

21665313 is a deficient number, since it is larger than the sum of its proper divisors (11578227).

21665313 is an equidigital number, since it uses as much as digits as its factorization.

21665313 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7278 (or 7269 counting only the distinct ones).

The product of its digits is 3240, while the sum is 27.

The square root of 21665313 is about 4654.6012718599. The cubic root of 21665313 is about 278.7757476535.

The spelling of 21665313 in words is "twenty-one million, six hundred sixty-five thousand, three hundred thirteen".