21315581 has 16 divisors (see below), whose sum is σ = 25276416. Its totient is φ = 17596656.

The previous prime is 21315571. The next prime is 21315583. The reversal of 21315581 is 18551312.

It is a happy number.

It is not a de Polignac number, because 21315581 - 2⁶ = 21315517 is a prime.

It is a super-2 number, since 2×21315581² = 908707986735122, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21315581.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21315583) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 21560 + ... + 22526.

It is an arithmetic number, because the mean of its divisors is an integer number (1579776).

Almost surely, 2^21315581 is an apocalyptic number.

It is an amenable number.

21315581 is a deficient number, since it is larger than the sum of its proper divisors (3960835).

21315581 is an equidigital number, since it uses as much as digits as its factorization.

21315581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1088.

The product of its digits is 1200, while the sum is 26.

The square root of 21315581 is about 4616.8800071044. The cubic root of 21315581 is about 277.2675585137.

Adding to 21315581 its reverse (18551312), we get a palindrome (39866893).

The spelling of 21315581 in words is "twenty-one million, three hundred fifteen thousand, five hundred eighty-one".