21243530 has 64 divisors (see below), whose sum is σ = 48771072. Its totient is φ = 6469440.

The previous prime is 21243527. The next prime is 21243533. The reversal of 21243530 is 3534212.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21243527) and next prime (21243533).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21243533) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 35897 + ... + 36483.

It is an arithmetic number, because the mean of its divisors is an integer number (762048).

Almost surely, 2^21243530 is an apocalyptic number.

21243530 is an abundant number, since it is smaller than the sum of its proper divisors (27527542).

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

21243530 is a wasteful number, since it uses less digits than its factorization.

21243530 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 659.

The product of its (nonzero) digits is 720, while the sum is 20.

The square root of 21243530 is about 4609.0704051902. The cubic root of 21243530 is about 276.9547989341.

Adding to 21243530 its reverse (3534212), we get a palindrome (24777742).

The spelling of 21243530 in words is "twenty-one million, two hundred forty-three thousand, five hundred thirty".