21581536 has 24 divisors (see below), whose sum is σ = 43031520. Its totient is φ = 10652928.

The previous prime is 21581533. The next prime is 21581537. The reversal of 21581536 is 63518512.

It is a super-2 number, since 2×21581536² = 931525392238592, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21581498 and 21581507.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21581533) 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, 1741 + ... + 6796.

It is an arithmetic number, because the mean of its divisors is an integer number (1792980).

Almost surely, 2^21581536 is an apocalyptic number.

It is an amenable number.

21581536 is a deficient number, since it is larger than the sum of its proper divisors (21449984).

21581536 is an equidigital number, since it uses as much as digits as its factorization.

21581536 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8626 (or 8618 counting only the distinct ones).

The product of its digits is 7200, while the sum is 31.

The square root of 21581536 is about 4645.5931806390. The cubic root of 21581536 is about 278.4159534171.

The spelling of 21581536 in words is "twenty-one million, five hundred eighty-one thousand, five hundred thirty-six".