21000065 has 4 divisors (see below), whose sum is σ = 25200084. Its totient is φ = 16800048.

The previous prime is 21000059. The next prime is 21000097. The reversal of 21000065 is 56000012.

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 4734976 + 16265089 = 2176^2 + 4033^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000065 - 2¹⁴ = 20983681 is a prime.

It is a Duffinian number.

It is a Curzon 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, 2100002 + ... + 2100011.

It is an arithmetic number, because the mean of its divisors is an integer number (6300021).

Almost surely, 2^21000065 is an apocalyptic number.

It is an amenable number.

21000065 is a deficient number, since it is larger than the sum of its proper divisors (4200019).

21000065 is an equidigital number, since it uses as much as digits as its factorization.

21000065 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4200018.

The product of its (nonzero) digits is 60, while the sum is 14.

The square root of 21000065 is about 4582.5827870318. The cubic root of 21000065 is about 275.8927022887.

Adding to 21000065 its reverse (56000012), we get a palindrome (77000077).

The spelling of 21000065 in words is "twenty-one million, sixty-five", and thus it is an aban number and an uban number.