21021165 has 24 divisors (see below), whose sum is σ = 39750048. Its totient is φ = 10191840.

The previous prime is 21021157. The next prime is 21021181. The reversal of 21021165 is 56112012.

It is not a de Polignac number, because 21021165 - 2³ = 21021157 is a prime.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 20739 + ... + 21728.

It is an arithmetic number, because the mean of its divisors is an integer number (1656252).

Almost surely, 2^21021165 is an apocalyptic number.

It is an amenable number.

21021165 is a deficient number, since it is larger than the sum of its proper divisors (18728883).

21021165 is a wasteful number, since it uses less digits than its factorization.

21021165 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42489 (or 42486 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 18.

The square root of 21021165 is about 4584.8844042135. The cubic root of 21021165 is about 275.9850732318.

Adding to 21021165 its reverse (56112012), we get a palindrome (77133177).

It can be divided in two parts, 210211 and 65, that added together give a triangular number (210276 = T₆₄₈).

The spelling of 21021165 in words is "twenty-one million, twenty-one thousand, one hundred sixty-five".