21150665 has 4 divisors (see below), whose sum is σ = 25380804. Its totient is φ = 16920528.

The previous prime is 21150659. The next prime is 21150671. The reversal of 21150665 is 56605112.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21150659) and next prime (21150671).

It can be written as a sum of positive squares in 2 ways, for example, as 10936249 + 10214416 = 3307^2 + 3196^2 .

It is a cyclic number.

It is not a de Polignac number, because 21150665 - 2¹⁸ = 20888521 is a prime.

It is a Duffinian 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, 2115062 + ... + 2115071.

It is an arithmetic number, because the mean of its divisors is an integer number (6345201).

Almost surely, 2^21150665 is an apocalyptic number.

It is an amenable number.

21150665 is a deficient number, since it is larger than the sum of its proper divisors (4230139).

21150665 is an equidigital number, since it uses as much as digits as its factorization.

21150665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4230138.

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 21150665 is about 4598.9852141532. The cubic root of 21150665 is about 276.5506448896.

Adding to 21150665 its reverse (56605112), we get a palindrome (77755777).

The spelling of 21150665 in words is "twenty-one million, one hundred fifty thousand, six hundred sixty-five".