21408165 has 32 divisors (see below), whose sum is σ = 38252160. Its totient is φ = 11359872.

The previous prime is 21408161. The next prime is 21408169. The reversal of 21408165 is 56180412.

It is an interprime number because it is at equal distance from previous prime (21408161) and next prime (21408169).

It is not a de Polignac number, because 21408165 - 2² = 21408161 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21408161) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 46617 + ... + 47073.

It is an arithmetic number, because the mean of its divisors is an integer number (1195380).

Almost surely, 2^21408165 is an apocalyptic number.

It is an amenable number.

21408165 is a deficient number, since it is larger than the sum of its proper divisors (16843995).

21408165 is a wasteful number, since it uses less digits than its factorization.

21408165 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 818 (or 812 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 27.

The square root of 21408165 is about 4626.8958276581. The cubic root of 21408165 is about 277.6684149340.

Adding to 21408165 its reverse (56180412), we get a palindrome (77588577).

The spelling of 21408165 in words is "twenty-one million, four hundred eight thousand, one hundred sixty-five".