21645165 has 32 divisors (see below), whose sum is σ = 37946880. Its totient is φ = 10486784.

The previous prime is 21645133. The next prime is 21645167. The reversal of 21645165 is 56154612.

It is a cyclic number.

It is not a de Polignac number, because 21645165 - 2⁵ = 21645133 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21645167) by changing a digit.

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 31 ways as a sum of consecutive naturals, for example, 5932 + ... + 8858.

It is an arithmetic number, because the mean of its divisors is an integer number (1185840).

Almost surely, 2^21645165 is an apocalyptic number.

It is an amenable number.

21645165 is a deficient number, since it is larger than the sum of its proper divisors (16301715).

21645165 is a wasteful number, since it uses less digits than its factorization.

21645165 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2981.

The product of its digits is 7200, while the sum is 30.

The square root of 21645165 is about 4652.4364584592. The cubic root of 21645165 is about 278.6893035481.

Adding to 21645165 its reverse (56154612), we get a palindrome (77799777).

The spelling of 21645165 in words is "twenty-one million, six hundred forty-five thousand, one hundred sixty-five".