21215565 has 48 divisors (see below), whose sum is σ = 42951168. Its totient is φ = 9485568.

The previous prime is 21215561. The next prime is 21215569. The reversal of 21215565 is 56551212.

It is an interprime number because it is at equal distance from previous prime (21215561) and next prime (21215569).

It is not a de Polignac number, because 21215565 - 2² = 21215561 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21215561) 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 47 ways as a sum of consecutive naturals, for example, 14089 + ... + 15521.

It is an arithmetic number, because the mean of its divisors is an integer number (894816).

Almost surely, 2^21215565 is an apocalyptic number.

It is an amenable number.

21215565 is an abundant number, since it is smaller than the sum of its proper divisors (21735603).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21215565 is a wasteful number, since it uses less digits than its factorization.

21215565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1498 (or 1495 counting only the distinct ones).

The product of its digits is 3000, while the sum is 27.

The square root of 21215565 is about 4606.0357141473. The cubic root of 21215565 is about 276.8332177285.

Adding to 21215565 its reverse (56551212), we get a palindrome (77766777).

The spelling of 21215565 in words is "twenty-one million, two hundred fifteen thousand, five hundred sixty-five".