21001165 has 4 divisors (see below), whose sum is σ = 25201404. Its totient is φ = 16800928.

The previous prime is 21001153. The next prime is 21001177. The reversal of 21001165 is 56110012.

It is a happy number.

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 (21001153) and next prime (21001177).

It can be written as a sum of positive squares in 2 ways, for example, as 16152361 + 4848804 = 4019^2 + 2202^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001165 - 2⁷ = 21001037 is a prime.

It is a Duffinian number.

It is a congruent 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, 2100112 + ... + 2100121.

It is an arithmetic number, because the mean of its divisors is an integer number (6300351).

Almost surely, 2^21001165 is an apocalyptic number.

It is an amenable number.

21001165 is a deficient number, since it is larger than the sum of its proper divisors (4200239).

21001165 is an equidigital number, since it uses as much as digits as its factorization.

21001165 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4200238.

The product of its (nonzero) digits is 60, while the sum is 16.

The square root of 21001165 is about 4582.7028051140. The cubic root of 21001165 is about 275.8975193639.

Adding to 21001165 its reverse (56110012), we get a palindrome (77111177).

The spelling of 21001165 in words is "twenty-one million, one thousand, one hundred sixty-five".