21815965 has 4 divisors (see below), whose sum is σ = 26179164. Its totient is φ = 17452768.

The previous prime is 21815939. The next prime is 21815987. The reversal of 21815965 is 56951812.

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 3308761 + 18507204 = 1819^2 + 4302^2 .

It is a cyclic number.

It is not a de Polignac number, because 21815965 - 2⁷ = 21815837 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2181592 + ... + 2181601.

It is an arithmetic number, because the mean of its divisors is an integer number (6544791).

Almost surely, 2^21815965 is an apocalyptic number.

It is an amenable number.

21815965 is a deficient number, since it is larger than the sum of its proper divisors (4363199).

21815965 is an equidigital number, since it uses as much as digits as its factorization.

21815965 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4363198.

The product of its digits is 21600, while the sum is 37.

The square root of 21815965 is about 4670.7563627318. The cubic root of 21815965 is about 279.4204210408.

The spelling of 21815965 in words is "twenty-one million, eight hundred fifteen thousand, nine hundred sixty-five".