21531365 has 4 divisors (see below), whose sum is σ = 25837644. Its totient is φ = 17225088.

The previous prime is 21531361. The next prime is 21531379. The reversal of 21531365 is 56313512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 5387041 + 16144324 = 2321^2 + 4018^2 .

It is a cyclic number.

It is not a de Polignac number, because 21531365 - 2² = 21531361 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531361) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 2153132 + ... + 2153141.

It is an arithmetic number, because the mean of its divisors is an integer number (6459411).

Almost surely, 2^21531365 is an apocalyptic number.

It is an amenable number.

21531365 is a deficient number, since it is larger than the sum of its proper divisors (4306279).

21531365 is an equidigital number, since it uses as much as digits as its factorization.

21531365 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4306278.

The product of its digits is 2700, while the sum is 26.

The square root of 21531365 is about 4640.1901900676. The cubic root of 21531365 is about 278.2000397613.

Adding to 21531365 its reverse (56313512), we get a palindrome (77844877).

The spelling of 21531365 in words is "twenty-one million, five hundred thirty-one thousand, three hundred sixty-five".