21500065 has 4 divisors (see below), whose sum is σ = 25800084. Its totient is φ = 17200048.

The previous prime is 21500029. The next prime is 21500069. The reversal of 21500065 is 56000512.

It is a happy number.

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 7354944 + 14145121 = 2712^2 + 3761^2 .

It is a cyclic number.

It is not a de Polignac number, because 21500065 - 2⁷ = 21499937 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21500069) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2150002 + ... + 2150011.

It is an arithmetic number, because the mean of its divisors is an integer number (6450021).

Almost surely, 2^21500065 is an apocalyptic number.

It is an amenable number.

21500065 is a deficient number, since it is larger than the sum of its proper divisors (4300019).

21500065 is an equidigital number, since it uses as much as digits as its factorization.

21500065 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4300018.

The product of its (nonzero) digits is 300, while the sum is 19.

The square root of 21500065 is about 4636.8162568728. The cubic root of 21500065 is about 278.0651685462.

Adding to 21500065 its reverse (56000512), we get a palindrome (77500577).

The spelling of 21500065 in words is "twenty-one million, five hundred thousand, sixty-five".