21390065 has 4 divisors (see below), whose sum is σ = 25668084. Its totient is φ = 17112048.

The previous prime is 21390043. The next prime is 21390071. The reversal of 21390065 is 56009312.

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 10214416 + 11175649 = 3196^2 + 3343^2 .

It is a cyclic number.

It is not a de Polignac number, because 21390065 - 2¹⁶ = 21324529 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, 2139002 + ... + 2139011.

It is an arithmetic number, because the mean of its divisors is an integer number (6417021).

Almost surely, 2^21390065 is an apocalyptic number.

It is an amenable number.

21390065 is a deficient number, since it is larger than the sum of its proper divisors (4278019).

21390065 is an equidigital number, since it uses as much as digits as its factorization.

21390065 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4278018.

The product of its (nonzero) digits is 1620, while the sum is 26.

The square root of 21390065 is about 4624.9394590632. The cubic root of 21390065 is about 277.5901392642.

Adding to 21390065 its reverse (56009312), we get a palindrome (77399377).

The spelling of 21390065 in words is "twenty-one million, three hundred ninety thousand, sixty-five".